Data Sheet for that PC If you find the power supply section, it says that it is a ATX Form. So yes,
ATX Power Supply is what you want.
You don't want to go cheap on a power supply. Like I had mentioned and gave a link to, Corsair, Antec, Seasonic, and CoolerMaster are reliable brands. Many of the cheaper power supplies do not actually supply the wattage they say they do.
Look at that link I gave you above for the Corsair PSU.
Here is a link to shopping results from pricegrabber for the 8800 GT.
HEREHowever similarly priced is the 9600 GT which is a better card.
HEREHere is a chart of many Power Supplies and how they are rated. Notice the legend at the top.
H = High Quality (Good Solid Reliable Brand)
L = Low Quality (Cheap Generic)
M = Medium Quality (In-between)
U = UnknownA-Power................L
A-Top..................L
A+GPB..................L
AcBel..................L
AC Ryan (Ryanpower)....L
Aerocool...............U
AG.....................L
Ahanix.................L
Akasa..................L
Allied.................L
Antec..................M/H
AOpen..................L
APC....................L
Apex Allied............L
Aspire.................L/M
Astec..................L
Athena.................L
BFG....................L
Broadway Gaming........U
Channel Well...........L
CHAS...................L
Chenbro................U
Chieftec...............L
Coba...................L
Codegen................L
Conrad.................M
CoolerMaster...........H
CoolMax................M
Crystal................L
Dell...................L
Delta..................L
Diablo.................L
Eagle..................L
Echo Star..............L
Enermax................H
Engleking..............M
Enlight................M
Epson..................L
FDK....................L
Fortron (FSP)..........H
Gateway................L
Gazelle Multimedia.....L
Global Marketing.......L
GPower.................L
Guardian...............L
Herolchi...............M
Hipro..................L
HP/Compaq..............L
HPC International......L
Huntkey................L
I-Star.................L
IBM Redundant..........U (expensive)
Intel Redundant........U (expensive)
In Win.................L
Jaguar.................U
Jantech…………..L
Kensington.............L
Kingwin................L
L&C....................L
Leadman................L
Levicom................L
LiteOn.................U
Logisys................U
Mad Dog................L/M
Maxtron................L
MGE....................L
MGE Vortec.............M
MorningStar............L
NEC....................L
Newton.................L
Nexus..................L
Noise Magic............L
NorthQ.................M
Nspire.................L
OCZ....................H
Omega..................L
Packard Bell...........L
PC Power & Cooling.....H
PC-World (PCW).........L
PCMCIS.................U
Power..................L
PowerStream............L
PowerTek...............L
PowerUp................L
PowMax.................L
PowMax XPower..........L
Premium................L
Pyramid................L
Q-Tec..................L
Q-Technology...........L
RaidMax................U
Real Power.............L
Rosewill...............L
SCS....................L
SeaSonic...............H
Shuttle................L
Silent Purepower.......U
SilenX.................L
Silverstone............H
Sky Hawk (Eagle Tech)..L
Sparkle................H
Star Micronics.........L
StarTech...............L
Sun....................L
SuperFlower............L
Supermicro.............L
Tagan..................H
Task...................L
ThermalTake............M
Topower................L
Tri-Mag................L
TSP....................L
Tyan Tiger.............L
TTGI...................L
Ultra-Power Computer...L
Ultra..................M
Ultra X-Connect........L
Vantec.................H
Verax..................H
Vigor..................U
Xion...................L
xPCgear................L
Zalman.................H
Zippy..................L
Hope that helps!