Will this System be Adequate?

Hi guys, I'm rebuilding my recent build as I'm not happy with it and was wondering what you think of the below spec and whether there is anything you would improve on. I'm not running on a huge budget unfortunately but here's what I currently have and what I'm going to be buying to work with:

Athlon 64 3200 (Venice Core) - Already have
Gigabye K8N Pro SLi Mobo - Going to buy
2gb Corsair ValueSelect RAM - Already have
1 x 200gb Maxtor DiamondMax 10 (16mb buffer) - Already have
1 x Optical drive - Already have
XFX Geforce 6600 (512mb) - Already have
Aerocool Turbine 450w PSU - Already have
Lexa Case - Going to buy
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Hiper 580w Type-R Modular PSU - Maybe going to buy


I plan to increase the RAM to 4gb over the next couple of months (more Corsair ValueSelect probably - would I notice a huge difference if I used better grade Corsair RAM?)

I'm considering changing PSU to a 580w Hiper Type-R Modular - anyone got an opinion on this or do you think I'd be fine with the PSU I already have?

I'm planning to use this machine mainly for gaming and a small bit of light office work. Will this be adequate for my needs?

What do you think of the XFX Geforce 6600 (512mb) ? I've found it's not too bad although the 3d Mark 05/06 results were nowhere near as good as I'd hoped. I'm going to overclock it and see how it performs then.

Any comments/criticisms/suggestions would be really welcomed!

Thanks

Sean

PS. Sorry for any typos!