RAM voltage

I have currently 2 gigs of Kingston HyperX 800Mhz memory in my system. Due to the stupidly low price of RAM right now, i was thinking of getting another 2 gig set, to make it so I have 4 gigs in total, 1 gig in each slot.
2 problems....

1) The RAM I have is rated at 2.0V. Pretty much all the RAM I can find seem to be 2.1 or something, basically not what mine is at

2) I heard that problems may arise from using all 4 slots on the mobo? I have a nForce 680i for reference, full specs are in my profile...

Any help is appreciated

Unfortunately, you cant be sure until you try.

As for the voltage, just let the motherboard decide. AUTO function and see what happenes

I'm sure that running your ram that's rated at 2.0V at 2.1V wouldn't cause a problem. There are plenty of 2x1Gb sticks that run at 1.8V and above.

You may need to increase the voltage of your northbidge in the bios if you run into stability problems. DDR2 is so cheap now, a high quality renowned brand will set you back the astonishing total of about £25+ for 2x1Gb.