just ordered 550 watt power supply as hp only furnished 300 and new card needs 400 watts which could be reason win 7 is so slow?
also looking into new board and chip for older hp tower Pavilion a1130n series - do you think i may upgrade to a p55 board and i5-750 chip in the old tower?

Windows 7 should run fine on the HD 4670. Must be that your PSU is failing to provide the required power to the card. Get the new power supply and see how it goes. Continuing to run the card on the 300W PSU may damage it permanently.

If you're intending to make a complete upgrade please give us a budget.

I'm at about $600.00 which includes Asus P7P55D MO, i5-750, 4G Ram, 750Watt PSU, CD/DVD burner, CD/DVD reader, WD 500G Blue, Antec 300 case and Sapphire Radeon HD4670 vga.............and three extra fans
What do you think - any recommended changes before I start to install?
Thanks

Save some money on the PSU(less watts, not less quality!)
And maybe you can save on the motherboard too.
Use this money to something else, like a better VGA

thanks, i'll look into that

How much is the motherboard coming to?

Also, which PSU have you selected. A few links would be helpful.

I got a good deal at micro center on a corsair 750 watt psu $89.00

the Asus P7P55D was $149.00