first of all... WHERE is the pain? Outside knee? Under the knee cap? Behind the knee? Inside knee? there are different issues that cause each problem! check out this link for more info!

http://www.roadcycling.com/training/kneepain.shtml



I had a serious issue with bike fit that I was unaware of... my saddle was WAY too low... and I was riding pedals with float... which in my case actually contributed to the problem! This is something I would NEVER have figured out on my own... and resulted in just over 2 months off the bike while I healed. I paid for a fit... best $200 I have spent on cycling... people often as shocked at the $ I spent on the fit... but I figure I had a bike that cost WAY more than that hanging on the garage wall since my knees were blown out and I couldn't ride... it was well worth it to be able to ride PAIN FREE!

good luck... I empathize having been there myself...