Looks like it's working properly now. Not sure why it was acting up before, but it looks like Operator Error (code ID 10 T, most likely).
Thanks to Rael for double-checking my copy of the blosxom.cgi file, to rule out any kind of serious problem.
I've now limited the number of entries on each page to 15, so it's not a 50K hit each time. There's also a category index on the left side now, as well as indices for each category (just change the index.html URL to index.index, and you'll get a list of entries).
I also modified my xml feed to wrap the entry text in CDATA, so it parses and validates properly for entries that have HTML in them.