I butchered my site in the upgrade and want to revert! Help!

I was trying to upgrade to WP 2.5 and messed something up. I then tried to go back to an earlier version and my database got screwed up: The categories were all deleted and the whole thing got screwed up (I can’t add them back) Luckily I backed up with wp=backup last week and have a sql file. How to I use that to revert everything? I’d like to go back to my previous version for now (2.2.1)
Thanks!