That solves the problem of the entire thread going wide, but messages with any long lines of PRE text in them are still breaking out to the left and right. You can probably get them to line up on the left if you do as Wayne suggested at vb.com and make the width of the thread column width="*", but I haven't looked at your source in any detail. If you want the author column to line up all the time, I think the only way is to throw in the spacer gif. I haven't found anything else that works.
BTW, I like these colors!