I have compiled a lot of kernels now :> the lates one was 2.6.5 and the problem is still there.. When i boot a kernel who have framebuffer on my Trident video accelrator, i'm getting two identical screens on the same monitor. What i'm using is a Satellite 6000 Pro laptop
Steps to Reproduce:
1.Turn on Power
2.Select the kernel i wanna boot (the one with framebuffer on)
3.The screen duplicate - splits
Normal screen ;)
If this problem still happens on the latest vanilla kernel sources (sys-kernel/development-sources-2.6.7), you should report it on http://bugme.osdl.org/. First you might want to check some of the tridentfb's options (Documentation/fb/tridentfb.txt) (if you haven't done it already). From what you've described, center/stretch, fp and nativex might be of some use here.
Other than that, I'm afraid we can't help you.