How to use "custom" map downloaded from web within COD 4 for PC? I'm a total beginner when it comes to gaming,

I'm a total beginner when it comes to gaming, but would close to to use some custom maps you can download from the internet. I've downloaded some already, but can't integer out how I can get to play them. I entail them for multi player mode, can anyone help me win started?

Thanks

Answers: try going to www.infintyward.com and check the forums? try looking for a custum map server