This is just an FYI for anyone that wants to do the same. You can mess up your adapter doing this, so be warned.
I have an ia1 that I want to use as a simple PC for my daughter (internet only). I followed all the instructions here and elsewhere and got it running with Midori (WildWildWes image). The only thing left to do was get a USB network adapter. I ran to a local store, but could not find any supported adapters. So I bought a NetGear FA101 in hope that I could get it to work. I opened it up and saw that it uses a Pegasus II chip. Good. I know that is supported. Plugged it in and of course it didn't work because the SID/PID are different than any of the supported cards. I knew that I could modify pesasus.c and add the PID/SID, but installing the build kit and recompiling the driver seemed like more work than it should be. I had read about other adapters being flashed to use a different PID/SID so I set out to try to do the same here. I located a utility to do it and have successfully changed the PID/SID to a supported Pegasus II adapter. It's works great now. Here's what I did:
1. Download http://www.admtek.com.tw/download/nic/adm8511/ADM8511_EEPATCH_100.zip from http://www.admtek.com.tw/index/index/download.htm. This zip file contains the CONVERT.EXE and SROMB.EXE files you will need.
2. Create a bootable floppy disk with system files on it ("format a: /s" from Win98).
3. Unzip the files to the foppy disk.
4. Edit the file vendor.h with the PID and SID that you want to use. I didn't change the values since the defaults are supported.
5. Edit the addr.now and addr.max files if you want a different MAC address. I was going to change it to the proper value from the adapter, but decided to leave it alone since it was a unique MAC for my network anyway.
6. Reboot computer from the floppy disk with the USB adapter attached. SROMB didn't work for me from Win98 which is why I created the DOS boot disk.
7. Run Convert.EXE.
8. Press any key to get passed the first information screen.
9. Press 1 to modify (convert) the file SROMB.EXE.
10. Hopefully you'll get a message saying it was Translated successfully.
11. Press 0 to exit convert.
12. Run SROMB.EXE and after a few seconds you will get a message back with a dump of some sort.
13. Your done. Try the adapter and it should work now. Good luck.