As mentioned, go for the cheaper RAM and get 2x2GB sticks to allow for more upgradability in the future.
Spend the extra on another 500GB hard drive, as raw AIFF + Wav files take up masses of storage and that space will soon dissapear. I have around 50 Cubase + Pro Tools songs and i use over 400GB just for these.
CPU wise, go for a Q6600. Most DAW's support Quad-core processors and it'll last you much longer than an overclocked dual. Thankfully the music industry has welcomed the additon of quad-core technology and so you'd be silly to go for a dual over a quad in this instance. As mentioned, theres no need to spend £150 on a motherboard unless you will make use of the extra features. Just go for a standard P35 or the newer P45's that will allow the overclocking of the Q6600 to a nice level. (ideally 3ghz or above). You may wish to get a 3rd party CPU cooler as well, if you want to get the best out of it.
I'd also go for a standard 8800GT over the GTS. The 8800GT is still a fanstastic card and will allow you to play all of the latest games at full settings, as long as you arent running dual 24" screens
As for the soundcard, DONT GO CREATIVE! I can't stress that enough. Not only are they awful for general PC usage, but they arent designed for music creation at all! Look at M-Audio, Emu and Edirol to mention just a few. These are soundcard with fantastic SNR's, lots of balanced I/O's and full ASIO/Kernal support for all DAW's. You want to spend around £200-300 on a good FireWire/PCI soundcard, and the same on some studio monitors. Of course it depends on what kind of music you wish to create and to what kind of professional level, but with a PC like that, you'd be silly spending as little as possible on the most important components for music production.
