I would think so since the database end isn't that different between the two. Though for the record I'd suggest an upgrade if only for the security fixes.
Oh, and before I forget, make backups before trying just in case.... (always a good habit, no matter how 'unlikely' a problem is )
Christine, extract the asp file from this zipped file, upload it to your server and execute it. It should fix the faulty topics and allow the archiving operations to proceed.
Got the exact same problem as the original poster. Any chance you could save me some time by reposting the "UpdateLastPostAuthor.zip" - the link you posted first time round doen't appear to work anymore - understandable given how long ago it was!