yep as the boys say you need a grunty pc..... the files are massive and compressed to hell. if you on a 2 year or older machine i guess your probably stuffed. as stated you need the correct codec. to play on windows media player. Also you need a pile of ram.
I edit on adobe elements. but its not the best.
Some hints. record different angles. as many as you can. board, helmet, line, kite, tripod. endless helmet cam is very hard to watch.
where possible do 10min max recording this limits the files size and makes for easier playback and editing.
decide what setting output you want. i record in 720p I can't see the difference in qaulity on my TV and lap top.
PS editing is a bitch it takes hours and hours to edit a small segment.... i recently edited this mountain bike trip at it took me about 20 hours.
Last peice of advice. Get a dedicated external hard drive as yourl end up with hundreds of gig of footage. I took 55gig on that one week mountain bike trip.