For future reference you can keep a copy of your bookmarks quite easily.
Thery are just links in a normal windows folder. For XP you will find it somewhere like this
C:\Documents and Settings\\Favorites
The is likely to be the user name that you use to log in. You might not notice this if you only have one user because you never have to log in.
So for example my folder is
C:\Documents and Settings\Nigel\Favorites
You can treat this folder and its contents just like any other windows folder - in that you can copy it to another place on the hard disk, floppy disk, USB Stick, CD etc. for backup purposes.
If you reinstall windows, get a new computer or just lose the contents somehow it just a simple matter of replacing the folder (and its contents) with your backup.
Cheers,
Nigel