Sorry to disappoint you, but a power supply won't change a thing. I have tried an Antec True Control 550, Antec True Power 430, Enermax 430, and CompUSA (PowMax) 500 w with no changes in the flickering. These were used in combination with 3 different systems.
AMD 6000+ X2
BFG Ageia PPU 128 pci
Audigy X-fi Audio pci express
Windows Vista Home Premium 32bit
Windows XP Pro 64bit