CTD/reboot issues with Q9400

I've just installed a new Q9400 in my Abit FP-IN9 motherboard (flashed to ver 16 per the website), after my previous E6320 (I think) worked flawlessly. But now I'm getting random crashes with software: both IE & Firefox while writting this & Filezilla (left on overnight to dl some large files, it got ~1/2 of them before CTD'ing). While I was installing some software, it came up with errors (which it hadn't last time I'd installed it with my dual core & is what I'm trying to download again).

The bios recognises the cpu fine, but it thinks that the cpu temp is ~90 degrees, which CoreTemp & RealTemp says is ~30 degrees, and my finger would agree with them.
Windows also recognises the Quad core cpu in both the hardware manager & task manager.
I haven't re-installed Windows since installin the new cpu.
The heatsink is seated fine.

My current set up:
Abit FP-IN9 motherboard bios ver16
Intel Q9400
2 Gig ram
600W psu
BFG 320Meg 8800GT
Win XP SP3

Any ideas? Should I press Scan.co.uk to take it back? If they don't find anything wrong with it, they'd charge me ~£10 & send it back. The Scan bloke I talked to said that Windows wouldn't recognise the Quad Core properly & that I'd have to re-install...

Thanks for any help/advice.