system -

k8n neo2 platinum (nforce 3)
2GB DDR ram
x1950 pro

I have the latest BIOS and MB drivers.

I just upgraded from an Athlon 64 3000+ to a 64x2 4400+. I'm not seeing much of a performance increase aside from what you would expect with the MHZ increase. The Bios and XP both recognize the dual cores but it's still my hunch that something's not configured right.

I'm only getting a score of 4,676 in 3dmark06 for instance which is a little less than half of what I've seen for similar systems? Infact 3Dmark 03, 05, and 06 all boosted only about 1000 points. (03 and 05 I might expect but 06 is multi-threaded from what I've read)

Bioshock is another example. I'm getting the same FPS, with all effects turned on, as with my old 3000+ an average of 20-30 fps. Infact when I turn off all visual effects I only get an average boost of 10 fps. This further leads me to think something's wrong with the CPU. I know my motherboard is a bit old but I doubt it's creating this kind of a bottleneck.

I followed all instructions in this thread - http://forum.notebookreview.com/showthread.php?t=60416
Any suggestions? Would a reformat and fresh install make a difference? Thanks.

Well, for whatever reason you're expecting to get a visual performance gain from your processor. Although it does play a part your expectations seem to be a little high. If you wanted your 3dmark score and FPS to increase by any noticeable amount you should of upgraded your GPU and not your CPU.

Open Device Manager and see if there's two CPUs in the list.
Try to run some CPU benchs like PCMark (not 3dmark).

I did try and run PCmark but the transparent window test kept failing for some reason. I followed the instructions (set desktop visuals for best performance and start menu must not be in classic mode).

edit - There are two CPUs in device manager. I just did upgrade my GPU by the way it was an x800 pro. I don't think my expectations are that unreasonable. It's not unreasonable to be confused when you see literally 0% performance increase in a supposedly dual-core optimized game like Bioshock. What did I spend my $135 for?

Sounds like a hardware issue for sure.. Your score does seem unusually low for the specs that you sumbitted.

I got Pcmark 05 working - 4,322. Apparently I'm the slowest computer in my range according to the website.