The 5900 is a piece of junk not just the flickering, but IQ sucks big time. Why dont you try your 5900 on a good CRT and see what happens.
Intel D875PBZ (Rev. 2) P4 3.0c @ 1%
1g p3200 crucial (2.5-3-2-6)
Antec truepower 550
Sony 21" G520P