Just find a camera that can be used with what you have and a separate microphone. The program you choose to use will have both peripherals work together.
I have a XP Pro Windows PC with a 2.5 ghrtz processor and 512mgb of ram, also my computer is about 5 years old. I want to get a camera and be able to see and talk with my friends and family over the net. I know that I'll need a camera with a built in microphone and they will to. I see this done in TV adds all the time "someone talking with someone else over the net", is it as easy as it looks or will I have to subscribe to a service to do this?