As you state, it might eventually be necessary to re-install XP. However, before doing that, it might be worth while investing a few pounds, at your local newsagent's shop, purchasing one of the many PC magazines available. Just look through the list of contents of the cover disks and you're almost certain to find one which includes IE7 or, better, Firefox.
Once you've installed a browser, from the disk, you'll be able to get back online and attempt to sort out any remaining problems.
Chris