switching locations (but keeping same main domain) hurt current SEO?

[Staxed]

I have a forum that currently has Page Rank 5, about 5000 uniques per day, and some other decent stats...

it is currently set with vbadvanced as the homepage domain.com/index.php, and the forumhome is domain.com/forum.php

i don't really like it like this...for a bunch of reasons...but i won't really get into them all...

i would like to move the forum to it's own forum directory (in order to at a subdomain), i'll be adding subdomains for a blog and other things...so i want the forums to be the same format...

my concern is that doing this...the current links (indexed in google and such) for all the vbpages will change from domain.com/threaddisplay.php$alsdfjkdsjfljflsdj to forum.domain.com/threaddisplay.php$adsfjdsflkjdslfkaj

i've never done this before...and was hoping someone has had experience with it...

will this hurt my ranking and such?...

[TheRed]

How about adding some mod_rewrite (permanent moved) lines?

So that way you don't get duplicated content.

[Staxed]

where would I add the mod_rewrite lines at?...(i'm not a coder...so unsure of this...)

also...I actually didn't even think about duplicated content (glad you mentioned it though)...i was worried about SEs having to reindex all the new pages...and making all the old indexes invalid...but if there is a way to make all those pages redirect permanently that would be awesome