When installing RH7, it should autodetect the network card.

About 128 to 192Mb of ram should be fine.

The knowledge base should be up, we've been having some intermittant errors but it's working now.

Heres the article:
Installing RedHat 7.2 in Virtual PC 5 for Macintosh 

Issue: 

Installing RedHat 7.2 in Virtual PC 5 for Macintosh 

Solution:

This procedure is designed for the causal user; many of the advanced features in Linux will not be addressed here. Please check the Red Hat web site or manuals for additional information on advanced topics.

1. Start Virtual PC. Press "command+L" to bring up the Virtual PC List.
2. Click NewÉ. 
3. Enter a name in the PC Setup Assistant. For this procedure, the PC was named "RedHat 7.2". Click the right arrow to continue.
4. Select "Guide Me", and click the right arrow to continue..
5. Select Linux from the OS box and click the right arrow to continue..
6. The memory allocation doesnÕt need to be adjusted at this point, select No, and click the right arrow to continue..
7. Select "Create a new drive image", and click the right arrow to continue..
8. Select a location for the new disk image. If changing to a new location, browse to the location and click Select. Click the right arrow to continue..
9. Click Create Drive and click the right arrow.
10. Click the right arrow to continue at Modem Settings.
11. Click the right arrow to continue at Palmtop Device Settings.
12. Click Done.
13. From the Virtual PC list, select the newly created image, and click Settings. Select "Virtual Switch" if Linux will be connecting to a network or acting as a server for other systems. Click OK. Click Start Up. 
14. Once started, the system message, "Boot Failure-Press any key to continue" will appear.
15. Insert the first Red Hat 7.2 cd-rom into the cd-rom drive, restart the guest OS. To restart, click Control, then Restart.
16. Click Restart, then press enter and the installation process will start.
17. Select a language, in this procedure, English, and click Next.
18. Select a keyboard, "Generic 104-key PC" is recommended for most installations. Select "U.S. English" and "Enable dead keys". Click Next. Other languages/keyboard models and layouts may work, but have not been tested.
19. Select a "Generic 2 Button Mouse (PS/2)" and click Next.
20. Click Next. Select the install type. For this procedure Custom was used.
21. Select Custom, and click Next.
22. Select "Have installer automatically partition drive for you" and click Next.
23. Click Yes to initialize the drive.
24. Leave "Remove all Linux Partitions on this system" and click Next.
25. Click Yes after the warning
26. Click Next on the summary of the Disk Setup.
27. Select GRUB bootloader and click Next. Leave the Bootloader password blank and click Next.
28. For this installation, the default Network Configuration was used. If no DHCP server exists on the network Linux will be connecting to, the proper TCP/IP information must be entered. Click Next.
29. Verify the type of firewall configuration and security level to be used. An explanation of the levels of security is provided in the windows to the left of the installation screen. For this installation, the default, Medium and "Use default firewall rules" was used. Click Next.
30. Select languages to be installed. Only English, the default, was selected for installation. Click Next.
31. Select the correct time zone. "America/Los Angeles Ð Pacific Time" was used for this installation. Click Next.
32. Enter a root password and confirm it. 
33. Create at least one additional user. Click Next when finished adding users.
34. For this installation, the Authentication Configuration defaults were used. Please consult with the network administrator for any additional information regarding authentication information and servers. Click Next.
35. Select additional Package Groups for installation. For this installation, "Printer Support, Classic X Window System, Gnome, KDE, Sound and Multimedia Support, Network Support, Messaging and Web Tools, Graphics and Image Manipulation, Games and Entertainment, Dialup support, Emacs, Windows Compatibility and Interoperability, and Utilities" were selected. Click Next.
36. Select S3 Trio64 (generic) for X Configuration. The default memory should be 4MB. Click Next.
37. Click Next to begin the installation.
38. When prompted for the second disk, insert the disk and make sure that Virtual PC captured it, the cd-rom icon should not be grayed out, if the cd-rom was properly captured. To manually capture the disk, right-click on the cd-rom icon and click "Capture Host Drive X:". Click OK to continue.
39. Bootdisk creation: to skip select "Skip boot disk creation". To create a book disk on a physical floppy disk, simply insert a blank floppy and click Next. To create a boot disk with a virtual floppy disk image:
a. From the Virtual PC Menu, click "Window then Virtual Disk Assistant."
b. Select "Create empty floppy or hard disk image" and click right arrow to continue.
c. Select "Create floppy disk image" and click right arrow to continue.
d. Click Create Image.
e. Enter the location and name for the disk, RH72boot was used for this installation. 
f. Click Save and click Done to finish.
g. Capture the floppy image by control-clicking the floppy icon and click "Capture Image".
h. Browse to the floppy image fileÕs location, select it and click Open.
40. In Red Hat 7.2, click Next to create the boot disk.
41. Select Unprobed Monitor with a horizontal sync of 31.5-48.5kHz and a vertical sync of 50-70Hz. Other values and monitors may work, however these are untested and make the screen output unreadable or cause damage to the monitor (use other values at your own risk.) Click Next.
42. Select a screen resolution, "High Color (16 bit)", "1024x768", KDE desktop, and Graphical login type were used for this installation. 
43. Click Test Setting, to verify X config, if screen is not readable or undesirable, change resolution or colors and try again. If you can see the message properly, click Yes. Click Next.
44. When the installation is complete, click Exit. Remove any physical media and/or release the cd/floppy image(s). To release a floppy image, right-click on the floppy icon in the lower left corner and click "Release RH72boot". 
Installation takes approximately 1.5 to 2 hours on an iMac G3 400.