If you're sitting in your computer chair thinking, "I think I'll finish reading this internet post, then I'll install the EVE Online expansion update on my computer." Stop. Don't do it! Keep reading this post for ever and ever.
According to the game's developers, some XP users are reporting problems with their boot.ini file after the upgrade. This problem won't brick your computer or anything, but it will be a pain to fix.
The EVE developers are very sorry. Check this page for up to the minute info on this issue, and fixes.
Gamespot.com: Eve Online Trinity breaks PCs