Moving from Subdomain to Subfolder without loosing seo

[Snowball1]

my forum is currently on a subdomain forum.domain.com but I will like to move it to domain.com/forum. I have several pages indexed in search engines and I don't want to loose that. Is there a way I could redirect all the old forum links to my new forum link without messing things up? Thanks very much

[ChopSuey]

Dont delete the subdomain, keep it. Just changed the Site Name/URL/Contact Details. :)

[Snowball1]

I renamed the folder and redirected the old folder to the new one for seo purposes. Initially the url was forums.mysite.com and now the url is mysite.com/forum . I use .htaccess to redirect forums.mysite.com to mysite.com/forum. I also used ErrorDocument 404 to redirect all error pages to mysite.com/forum. My only problem now is how to redirect the old threads which are already listed in search engines to my new urls. I have several pages indexed in search engines and I don't want to loose seo. is there a way to redirect all the old threads to their new threads without loosing seo? Thanks