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 :D