ATI 4770 on a 400W PS?

Depends on what the specs of your power supply are. You need to know the Amps or Watts on the +12v Rail/s

Mactronix

Power Supply Features
a)Proprietary IC & unique design
b)Embedded thermal sensor
c)Low-noise variable fan
d)Various safety protectionCP(over-current),OVP(over-voltage),SCP(short-circuit),UVP(under-voltage),OPP(over-power)
e)Output Connectors:
-20+4-pin MB connector
-Peripheral power connector x 4
-Floppy power connector x 1
-Serial ATA connector x 1
-P4 connector x 1
f)Cooling:80mm low-noise fan
g)MTBF:50,000 Hours
h)Votage Output:
+3.3V@20A;+5V@14A;+12V1@14A;+12V2@13A;-12V@0.3A;+5VSB@2.5A
+5V & +3.3V combined 130W MAX
+5V & +3V & +12V combine 385W MAX
TOTAL OUTPUT 400W MAX
h)Aproval:UL, CSA, FCC
i)Dimension:5.5" (D)x 6.0"(W) x 3.3"(H)

Thanks guys I might give it a go..

I have a new dell studio 540 (350 w PSU) with a 4770.
Catalyst 09.5 - 8.612..
Q8200
3070 Mb
Windows Vista ver. 6.0
Score 4153 o3 Marks
Resolution: 1680x1050(FS) - MSAA: 0X
FPS: min=61 max=97 avg=69