You can buy a can of air-con anti-bac spray in Consort (or any good motor factors) for around 15 quid that you just turn on in the car with the air-con up high for about ten minutes (little bit messy afterwards, but It worked for me).
JD
I used a can of Conna I think it was a/c cleaning spray a while back, and its been fine until recently, noticing the musty smell in the air con coming back a bit now.
Got it in Halfords when I was in Dublin last (jeez been a while! )
thanks lads, got stuff today called "cyclo air fresh", turned AC on full, closed windows in car, let it run for a minute or two and sprayed it into the vents under the wipers, car smells sweet now