I've replaced the 3Com with a DLink DFE-530TX+ 10/100. The card comes with a .c driver file, and easy installation instructions. In the process of getting this set up, I realized I'm running kernel 2.4.31, and the CDs I have only have the headers for 2.4.18.
I assume compiling against the wrong version is A Very Bad Thing, and likely to Cause Much Horkage. I did some poking around ftp.debian.org and ftp.kernel.org, but I have no idea WTF I'm looking for - a simple nudge in the right direction would be much appreciated.
For the record, I'm mainly sticking with this bullheaded experiment because I want to learn, not because I have huge hopes in it working. I have learned a lot doing this, which is why I want to follow it through.