I use the same stick, and have no problems. I've had 3 of them and they've all held calibration fine.
The first one, I calibrated basically once.. and only when replacing it (static killed it) a year later that I calibrated again. I do NOT use any saitek software. I am running WinXP Pro.
If you have 2 pairs of USB ports try plugging the stick into the other pair.
Also what is sharing an IRQ with your USB?
SKurj