major upgrade time

Hi, I haven't used these boards in a while, but I know that you guys know a LOT more about computer hardware than me. I am just about to upgrade my pc. Here is the list of components i am thinking of buying, and the prices (all from UK ebuyer and excluding VAT):

MSI 1950XTX 512MB VIVO 2XDVI PCI-E £280

Asus A8N-SLI SE Socket 939 Nvidia NF4 SLI ATX - Sound, Giga Lan USB 2.0 1000MHz FSB SATA £49

AMD Athlon 64 (ADA4600BVBOX) X2 4600+ socket 939 Dual Core 2.4Ghz 512kb and 512kb Cache £133

Kingston 1GB 400MHz DDR PC3200 DIMM 3-3-3 £60.85

I already have a 1g of 3200 memory (i think it is 3200, forgot how to check). Is it better to get more 3200, or is it better to just get faster memory? Not sure if 3200 memory will bottle neck performance!
I might also get a new case, but unsure what PSU i need (i have only one hard disk to power).

Thanks for any advice. My budget is around £600.

Also, is it simple to set up the dual core processor? Does it automatically use both cores or do you need to mess around in bios??

dual cores automatically "set up".

2 gigs of ram is good. I think your setup is great. Although, you may also concider a E6300 and a DS3.

However, the conroe path would be more expensive and you wouldn't be able to use your existing stick of pc3200.

3200 will be stock for socket 939 stuff BUT you wont be able to OC much with it. If youg et anything lower then PC 3200 then your board wil set up dividers for your CPU so it can run at a normal clock witht he slower ram.

Thanks for the advice. Not sure what E6300 or D3 means though. I am not planning to overclock the system yet, maybe when in 6-12 months time i will. Any advice on the PSU size? Will a standard 350psu case be okay?

That PSU might be enough for now, but if you plan on overclocking and adding a lot of harddrives and other little components within the system, then you might want to look for a little more power. 500W at least would be good, and give you a little headroom when you keep adding stuff to the system.