how to record skype and gameplay?

Generally a program that records sound is not every selective, so if for an example you're recording gameplay with sound, it will also record any sound coming out of Skype. The problem might be recording the sound that "you" make (i.e. if you speak to your friends the program might not pick this up). If this is possible depends on your program. I know that FRAPS is able to handle that bit (but NOT in XP. I guess that there's some technical limitations there, and it might well be true for other programs as well).

If you're having issues recording your own voice, you might have to use some other program and synch up the sound (this has the advantage of it being easier to change your sound volume, in case it's too high or low. You can hear how your friends are in comparison to the game as you play it, but you can't hear yourself).