Won't Go Straight

OK, another problem I'm having with CFS3 is all my planes won't go straight. I seem to drift slightly to the left during level flight (and thats not a big deal-barely noticible) but the real problem is taking off this way. I can't stay on the runway for very long and on some airfields there are buildings in the way I have to try and avoid (and that can be really hard at times). Has anyone else had a problem like this? I was thinking it may be with my joystick but this is the only game its been happening in (FS2004, B-17, and IL-2 work perfectly). If it helps, I'm using an original style sidewinder joystick.