My idea for an upgrade to my current build. Thoughts?

This is my current setup...

OS____Windows XP Home SP2
CPU___AMD Athlon X2 3800+ / 2.4GHz
Mobo__GIGABYTE GA-M61P-S3
GPU___GeForce 7600GT, 256MB GDDR3
RAM___A-DATA Extreme, 2GB, DDR2 800 / 4-4-4-12, 2T
PSU___FSP Group 450W, 36A
HDD___Western Digital Caviar 250GB
Case__Antec Nine Hundred

This is the setup I was thinking of upgrading to (in time)

CPU - AMD Athlon X2 5000+ Black Edition (OC'd to 3.2 GHz)
GPU - GeForce 9600GT SLI
Mobo - AM2+ and SLI compliant

Assuming all other components remain the same (case, OS, RAM, PSU and HDD), about how much would I expect to spend on this kind of upgrade and how big of a performance boost could I expect? Also, any suggestions for an Intel setup instead?

Note - Right now I game on a 19" (I think) monitor that does 1280x1024 max resolution, but I eventually want to game on a 24" monitor that gets 1920x1200. Added cost?

CPU 5000+BE: http://www.newegg.com/Product/Prod [...] 6819103194
$98

MB: http://www.newegg.com/Product/Prod [...] 6813138081
$80

Vid: http://www.newegg.com/Product/Prod [...] 6814130328
$180 x 2

I recommend waiting to see if a newer SLI board comes out for AM2+ (or just go with a 790FX and ATI cards)