£1500 should sort you easily if you already have the monitor.
The new chipset - do you mean Nehalem? Nehalem should be released fairly soon, however, you may just be better off buying a Quad when they get cheap.
http://3xs.scan.co.uk/ShowSystem.asp?SystemID=491
Would that do you? You can customise it a bit to suit what you want. It's not watercooled but it should easily be enough cooling for what you want. If you change the case to an Akasa Mirage/Eclipse the price will be almost exactly 1500.
It's got a Corsair PSU, XFX GTX280 (will easily handle what you want), 45nm Quad, 4GB RAM, etc.