Redirecting domain.com/thread to domain.com/forum/thread

[PJKCards]

Hello,
I recently moved my forum from www.domain.com to www.domain.com/forum.

Now all the links in old posts that link within the forum don't work. Is it possible to have all old URLs redirected?
For example:

http://www.domain.com/showthread.php?t=1000

Would direct to:

http://www.domain.com/forum/showthread.php?t=1000

Is there is way to do this? If not, are there any alternatives to make these old links be re-written?

Thanks

[PJKCards]

Anyone have any ideas? There are tons of links like this on my forum, and members hate being re-directed to the homepage since the URL isn't correct.

[Zachery]

I'm still learning my URL re-writing syntax, but I believe you should be able to accomplish what you want with the following

Options +FollowSymlinks
RewriteEngine on
RewriteRule ^showthread\.php$ /forum/showthread\.php$1 [R=301]

This is untested, and while it shouldn't cause any permanent issues, caution is advised.