Well, I have the same microphone, on the system below- I'm using the onboard Realtek codec. Using Windows 7 Pro (ordered from MS).
I've had trouble getting microphones working right; particularly, if I go into Counter-Strike, I had to run Ventrillo as Administrator, or it would not respond to the PTT key- that's while the in-game voice works fine. I know that this issue isn't the same as yours, however, while 7 has been mostly bulletproof, these issues have been popping up.
Canon 6D|24-105/4L |70-300/4-5.6 IS USM|50/1.4 USM|50/2.5 CM|50/1.8 STM|85/1.8 USM|Samyang/Bower 14/2.8|24/2.8 IS|Sigma 150-600 | C
Canon EOS-M|11-22 IS|22/2|EF-M 18-55