How can I send a variable I've dynamically set in PHP to my htaccess file?

I'm making a forum, and instead of having /forum/thread/1.htm like I do now, I want to be able to fetch the post title and put that as the URL, so it would be /forum/thread/title-of-thread.htm like vBulletin.

I know it's possible, I've just messed around so much I can't get it. Here's what I have now. This is what gives you /forum/thread/1 (thread.php?threadID=1).

RewriteRule ^([0-9]+)(|.(htm(.*)|php|cgi|thread|post|topic))$ thread.php?threadID=$1

With a few added stuff, like /forum/thread/1.topic or 1.post. For those of you who don't get that, here.

RewriteRule ^(.*).html$ thread.php?threadID=$1

*Simplified

Any help it appreciated!

Thanks,

-PG

How can I send a variable I've dynamically set in PHP to my htaccess file?

You can't! .htaccess is parsed before PHP even starts.

Ah, ok. Looks like I'll have to find another way around it :P