Hi all, thanks for all your help so far, it's going quite well! Here's an update:
Managed to clear the airbag warning light using the diagnostics & my laptop
Fitted the auxilliary belt and hey presto, no more squeal - thanks rugbymike
For anyone looking for a 'how-to' on the 2.0 drive belt, all you have to do is remove the cover on the top - the long thin black one with a 10mm socket and two allen keys, then remove the drivers wheel and inspection hatch which is covered by a couple of cross-head screws. Then you can see the pulleys if you look up - the tensioner is the only one with a socket visible (15mm as rugbymike said) - just give that a good twist anticlockwise and the old belt can be pulled off. Refit the new one in the same way. Just make sure you see which way the belt is running before you take it off!)
Have changed the wipers & given her a darn good clean inside & out.
I've booked her in for MOT now so hopefully it goes through!
I've still got some issues to iron out though. The main one being the air-con. I've re-gassed the system but the gas vanished within a day, so there's obviously a leak somewhere - is there a specific hose or area thats prone to leaks?
Second slightly easier issue is the drivers rear electric window doesn't work. I thought it was both windows, but it's just the offside one. I've tried to move it by hand & it's too hard. Is it easy to get the doorcard off & check?
Thanks for all your help so far, it's really appreciated!