Have a look in Documents and Settings/Your Name/Application Data/Thunderbird/Profiles and see if your mail folder is still intact.
If so you may not have lost your emails.
I would then use Mozbackup click here to back up your profile to a safe location.
Now uninstall Thunderbird and delete the above folder in Documents and Settings.
Reinstall Thunderbird 2 and again using Mozbackup restore your saved profile.
Hopefully that may work but if you have corrupted your profile then it may still be possible to save your emails by ,after reinstalling Thunderbird 2, just copying and pasting the mail folder from the saved profile into the new profile created by the new Thunderbird installation.