Yeah, be sure to check that the mic is selected as the input device for recording.  WinXP has a real bad habit of "helping" you by changing it to "line in" for recording anytime you play a CD, or especially if you rip CD's to MP3 etc.
I have gotten in the habit of checking it every time before logging in to fly, and keep both the volume control for windows and for Soundblaster [I am a x-fi victim donations accepted 

 ] in my hotbar as on my comp either one can change settings without notice.
Just one of many little things WinXP will "help" you with.  I wish there was a check box for "I don't need your help"  
Blackwulf