Typical first time build questions

This is my first computer build and I'm pretty tight on funds (I only have around $500)
Im going to be getting an old dell xps 400 for free so i'm going to try and use as many parts as i can from that (not many)

The only thing I'm really going to use are basics like operating system, hard drive, monitor, mouse, optical drive, and keyboard
Now heres the stuff I think im gunna buy. If you see any compatibility problems or if you know any cheaper/better parts please reply. Thanks in advance.

Computer i'll be getting http://support.dell.com/support/edocs/systems/xps400/sm...

New Parts:
Motherboard/Cpu: I'm thinkin either
http://www.tigerdirect.com/applications/SearchTools/ite...
or
http://www.tigerdirect.com/applications/SearchTools/ite...
(is the extra money worth the upgrade?)
~~~
PSU/case
http://www.tigerdirect.com/applications/SearchTools/ite...
or
http://www.tigerdirect.com/applications/SearchTools/ite...
~~~~
Video Card: Im thinking either
http://www.tigerdirect.com/applications/searchtools/ite...
or
http://www.tigerdirect.com/applications/SearchTools/ite...
(The fact they look the same is just a coincidence i dont care how it looks obviously, also the Wattage on the Radeon HD 7770 seems to be a lot more and when combined with the better CPU they are right on the limit of the PSUs im looking at. Is that a problem?)
~~~
RAM
http://www.tigerdirect.com/applications/SearchTools/ite...