Memory timings

Download and run CPUZ. Select the SPD tab and cycle through your sticks of memory. You should see at least a couple different settings for each, see if there is a setting that they all share.

Did you immediately go into the manual settings after installing? If you reset the board it will find settings for the RAM that should be compatible. After finding a base setting for them you can then try and manually improve the settings.

The JEDEC specification for DDR 400 is 2.6v so that's where I would start.

Try increasing voltage to at least 2.80V.

The CPU-Z application is crashing my computer when I'm on the page to view the different slots of memory, any idea why? The computer is stable otherwise.

I've had that happen before, I would suggest uninstalling it and reinstalling it.

i don't think u can run different size sticks like that. if you are going to run 4 sticks of memory. they need to be the same size, such a 4x1gb or 4x512 .

Nah, you can run 2x1GB and 2x512MB to get 3GB, lots of people do it. But you can have motherboard problems running "any" set of four modules, since it's harder to get four modules stable.

Not directly related to your hardware, but this reminds me of two similar cases in the past.

Intel's i815ep has 3 Ram slots, offers CL2 and CL3 timings, but the data sheet tells that the Bios should switch to CL3 if it detects 3 Ram modules, as the i815ep's buffers can't move heavy loads that fast. I don't know which mobo manufacturer followed the recommendation then. You could have a look at the P45's data sheet.

Asus did a nasty trick on the falsely praised TUSL2-C (with said i815ep). As soon as the user put the FSB over ~145MHz in the Bios (instead of 133MHz) the Bios switched the Ram to 3-3-3-7 and the AGP to 2x, without any remedy within the Bios' settings. Tweaking had to be done from special Windows applications.