HELP!!....i know nothing about cars!

I have a 2003 Golf 1.9TDI PD 100 (i think) with about 54k miles on it.

I was accelerating in 5th gear recently (roughly 2000 revs) and the engine appeared to 'over-rev' ie. rev counter shot up with no extra acceleration (or deceleration). I eased off and everything returned to normal. There was no shuddering (as most people on this site seem to mention).

I've managed to reproduce the problem (in lower gears) 2 or 3 more times by accelerating hard, but it is very intermittent.

I friend suspects its the clutch/flywheel on its way out. Does this sound right? How long might it last before failing? Or is it just a 'glitch' that might go away?

The car is still under an Approved Used Dealer warranty (by about 10 days!!!) - would it be covered?

Rgds
PAW