RAM OC voltage
I currently have 1GB (2X512) of DDR2 800 corsair TWIN2X1024A-6400 running at 4-4-4-12 timings at 1.95V (stock 1.9V). I am considering adding 2GB more to my system, however most 4-4-4-12 parts run at 2.1V. Is it safe to use this voltage on the sticks I have? What are the safe voltages for these parts? thanks.
Check with Corsair and see if it voids the warranty, I highly doubt it will. Probably covered to 2.3v or so.
They will run fine at 2.1v and it should be safe to do so.
The others may run at 2.0v perfectly stable too, so you could comprimise and meet in the middle, but I wouldn't hesitate to run them at 2.1v.