Me and the bro's have a little amateur video production crew called OneShot Productions (
http://www.oneshotproduction.net/) and we've made several feature length action sports type films. We use Windows PC's with Sony Vegas Pro (V4.0-9.0 depending on who's editing what) and it works killer. Vegas is mid priced ($300 for pro, $80 for studio) and very powerful (I'd go with pro). If you want to learn a kick arse tool for the PC thats pretty intuitive I'd say that Vegas is the way to go. Lots of great support sites and tutorials out there on the web too. Lastest versions have support for HD. I took some HD footage this summer but haven't tried editing anything yet, so I can't get perspective there.
I haven't used Adobe Premier since 4.0, but I always found it much more difficult top use and the price tag ($900+) was hard to swallow. If you got all the money in the world and you wouldn't rather mod your sled, then do what Richie Rich does and buy a Mac with Adobe Premier..that's pro. Ask that smug Mac Genius guy. He's a snappy dresser. Else be like the common man, grab a half rack of Coors, build a $500 PC with as much RAM, HD space, and Processor as you can afford, pick up Vegas, pops them Keers, and have at it.
With that all said, it don't mean nothing until you get quality footage. Cams, perspective, good riders/subject matter, shooting in snow conditions, and other filming nuisances is a whole nother ball of wax.