Advice Wanted for 1st Build PC

I am planning to build a pc that will be able to run music software smoothly, like Propellerheads Reason and Cubase at the same time. Also as a casual gamer a pc that can handle new games effectively, however i am not over enthusiastic about the best graphics and fraps but i would like a motherboard that i can upgrade during the next 2 years or so.

My budget is tight at around $500 - $600 for the initial build.

I am thinking about building an AMD system. I already have a monitor, speakers, keyboard, mouse and 500Gb WD SATA Drive.


After a few of days of research this is what i am planning:

Antec Three Hundred Tower
http://www.amazon.co.uk/Antec-Three-Hundred-Tower-supply/dp/tech-data/B0017Q8IAA/ref=de_a_smtd


Colors-IT 650w PSU
http://www.amazon.co.uk/Colors-650w-Titan-Power-Supply/dp/B0016ZUDY6/ref=sr_1_5?ie=UTF8&s=electronics&qid=1264321642&sr=8-5

Gigabyte GA-MA785GT-UD3H Motherboard
http://www.amazon.co.uk/Gigabyte-GA-MA785GT-UD3H-Motherboard-Gigabit-MA785GT-UD3H/dp/B002K8L374/ref=sr_1_2?ie=UTF8&s=electronics&qid=1264328897&sr=8-2

AMD Phenom II 550 - Black Edition
http://www.amazon.co.uk/AMD-Phenom-Cache-Dual-Processor/dp/B002BFOCW4/ref=sr_1_1?ie=UTF8&s=electronics&qid=1264319177&sr=1-1

Kingston Value Ram 2Gb x2
http://www.amazon.co.uk/Kingston-Value-800Mz-DDR2-NonECC/dp/B000Z2GO2Q/ref=sr_1_2?ie=UTF8&s=diy&qid=1264320337&sr=8-2

Asus Radeon HD 4650 1Gb
http://www.amazon.co.uk/Asus-Radeon-PCI-E-LP-Graphics/dp/B002KF3U6Y/ref=sr_1_4?ie=UTF8&s=electronics&qid=1264326653&sr=8-4

Edimax EW-7128G Wireless LAN PCI Card
http://www.amazon.co.uk/Edimax-EW-7128G-Wireless-802-11b-Ralink/dp/B000KLNRBS/ref=sr_1_12?ie=UTF8&s=electronics&qid=1264327814&sr=1-12

Microsoft Windows Vista Ultimate Edition -- What are the benefits of 64bit OS?



This is my first build so i am likely to have been naieve so could you advise me please on what you think about my choices and also anything that i have missed or will need to consider.

Thanks,

Ash