aircon screeching

[shaggy]

i noticed when i first start the car with the aircon on or turn it on when driving at over 30mph there is a screech (like a fan belt screech)
when i looked under the bonnet i have found it is the aircon pump pully
when i rev the engine the centre of the pully stops turning screeches then starts to turn again when the revs drop

is there a fix for this without having to buy one of these? http://www.toyotahilux.com/?doc=16&cid=152&vid=930
is there any way to adjust the clutch at all?
there are a couple of second hand pumps complete on ebay at between £20-£30 each but im concerned the problem will return with second hand

edited to say that the belt could do with tightening up but its not that loose

cheers in advance guys

[marky]

Check the tension of the belt 1st & adjust if required

[shaggy]

ive tightened the belt and it has stopped the screeching
but
on tick over the clutch just stops then restarts with a click and i can hear another fan kick in
im presuming this is normal?