The videos would need to be in a quicktime format to play on the iphone (it doesnt support flash).
The rest of it would be pretty easy really, i don't even think an 'app' would be needed. just a version of the site and forums that is formatted for a mobile device. i bet vbulletin even has a iphone addon out there ..
edit: actually here is one:
http://www.vbulletin.org/forum/showthread.php?t=171947