Buying a PC - is this a good purchase?

So I've been out of the PC world for a good long time now, and I'm in the market for a machine that I will mainly use for composing/recording and mixing tracks. Ideally I would buy a Mac for such activities, but ideally I would also win the lottery haha.  
 
I found this tower online for what I thought was a pretty good price, but I have no idea about a few key things. I mean, has Quad Core come into its own now? Would I be just as good with a Dual? And is a 9500 a decent enough card for rendering wave spectra pretty promptly?  
 
I probably sound like a dinosaur here but I really have been out the game for a while now with regards to PCs haha. 

Power supply seems pretty weaksauce, everything else is ok.

How many VST/DX plugins do you use? If it's not that many, you probably don't need a quad core. That said, if your DAW supports quad cores, then it definitely can't hurt to have one. My dual core E8400 is under 50% load constantly in a project with 4-5 tracks in Sonar. That said, there are about 4-5 instances of Guitar Rig, some compressors, a few synth VSTs etc all loaded at once... so needless to say I haven't optimised my project whatsoever. For someone with a bit more experience in that regard, it probably wouldn't be too bad at all.
 
The 9500 won't play games very well at all, but it should do what you want to do just fine.
 
As the above said, the PSU is a bit weak. Couldn't hurt to upgrade to the 500W.

" @Lashe: 700w would be way overkill, it's something used to run 2 ATi cards in CrossfireX or two Nvidias in SLI. "

Awesome stuff, cheers guys. Will be ordering this one up with the 500w then in the next few weeks!

" @cinemandrew: an i5 or i7 would be great to be sure, but they're a little out my budget to say the least -- life of a student, bane of my existence! A memory upgrade can be added as and when I need it I reckon though -- when I last checked 4gb RAM wasn't too bad for audio rendering haha but I may be just behind on the times.  "

I'd recommend getting a 650w PSU and maybe a slightly better GPU then that's pretty much set to go.
 
And of if you really wanted you could get an i5 CPU, the benefit wouldn't be immediate but it would future proof it abit. Not bad at £150 really, I can understand the budget constraints being a student myself but it's worth a few shifts working at the SU IMO.
 
Also: I've got a Q660 and I've hardly noticed the benefits for gaming but there are a few titles where I get a few extra FPS.