The "deal" works out to be $110 for the PSU, after the discount. And HEC is noted as a brand to avoid on the Power Supply Guide.
For a good PSU, look at this one:
Newegg.com - CORSAIR CMPSU-550VX 550W ATX12V V2.2 Power Supply 90 - 264 V UL, CUL, CE, CB, FCC Class B, TUV, CCC, C-tick - Power Supplies
$90, $80 after MIR
As for which card to get, the 8800GT or the 9600GT would not require changing your drivers (which is no big deal, actually). The 3870 and the 4850 are both sweet cards and are awesome as far as bang-for-the-buck. If it were me, I would go for the 9600GT or the 4850. In the end, though, it is your budget that will make the decision.