sounds like the clutch is going, probably the throwout bearing. I'd save up and get a new one soon. I'd either get an SVT one, or spend a bit and get a centerforce or one of those new ones that I think maybe SPMotorsports has...
2001 Mustang Bullitt
Dark Highland Green #0048
Performance by Ford Racing, Bassani, SLP, H&R and etc.
Former owner of a 99 Silver Frost SVT
GetOnItRACING