Not if you're using the ASRock board, it'll only support dual core Conroe chips and older. But if you choose to replace the mobo then a quad is definitely more powerful - it'll destroy your budget though...
it was meant to be cheapest possible, but if its worth getting quad then i may although id rather just get duo, shirty told me that the board is designed for conroe core 2 duo
Here is your CPU support list. E4500s and E6300s tend to be available for around £15 on eBay, and they do come up in the marketplace from time to time as well. You might even get an E2180 for a tenner.
what do you think of this http://www.ebay.co.uk/itm/Intel-Cor...Computing_CPUs_Processors&hash=item1c288908a7
hopefully they will come up, so this here is the best my mobo can take, very expensive though http://www.ebay.co.uk/itm/Intel-Cor...Computing_CPUs_Processors&hash=item3377a4a881
It's a good chip and at a reasonable price - that is what most auctions for the same chip end up at. However, it's a third of your budget! That's silly money for the X6800, it's a six year old chip now!
Is it ok to use the cpu without paste or even heatsink just to see if it works? and then quickly switch it off straight after