Have 6Gigs of RAM, OS shows 4. Help, please.

did you turn on memory remapping in the BIOS?

I would take your GSKILL out. You're mixing different RAM modules together which is never recommended. Granted yes they are both DDR2 800, however they are different sizes and timings are different. If I recall correctly, when you do this the 'faster' ram will slow itself up to match the 'slower' ram. So essentially your Crucials will run at 5-5-5-15 timings and slowing up your machine. It would be faster if you took the GSKILL out and let your Crucials run at 4-4-4-12. Its been a while that I've looked into this, but I'm pretty sure thats how it used to work. I wouldn't be surprised if the reason that your seeing 4gb is because your 2x2gb are even 'downsizing' to match the 2x1gb , ie not only are they lowering their speeds to match but also lowering their sizes as well so essentially you end up running 4x1gb sticks at 5-5-5-15 timings. thats my guess anyways, I havent kept up to date on mixing and matching RAM sticks as its always a bad idea when you do that anyways.

yup, I think you've got it. The only other solution is bad ram or bad dimms in the 1gb slots, but mixing ram will create all sorts of issues, especially with processors that have memory controllers.