Yea at least 4 gigs of ram and either a 7750 or 7770 would be sufficient. You should look to upgrade your machine at some point if your machine is using DDR2 memory chances are your processor is at least 4 years+ old I would look into it.
Yes it is able to yes. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 26 Amp Amps.)
Minimum 450 Watt for SLI mode system.
(Minimum recommended power supply with +12 Volt current rating of 28 Amp Amps.)
An available 6 pin PCI-E power connector (hard drive power dongle to PCI-E 6 pin adapter included with card)