Newbie memory question

I have this computer and with me running vista i belive i need more then 1GB of RAM so im going to go for 2GB, my question is can i use 2 different kinds of RAM if im going to be overclocking. here is my computer Below, Now i was wondering if i had to buy the corsair brand or could i go with a cheaper brand.

intel core duo E6300 2x 1.86GHz/2MB L2 cache
ASUS P5N-E SLI LGA 775 NVIDIA nForce 650i SLI ATX
CORSAIR XMS2 1GB (2 x 512MB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
GeForce 7950GT 512MB 256-bit GDDR3 PCI Express x16
Western Digital Caviar SE16 WD2500KS 250GB 7200 RPM 16MB

You can run different kits usually yeah, but your oc will be limited by the weakest of the 4 sticks. I recommend sticking with the same mem or at least some other ram with the same chips.

How far have you over clocked your current set of corsair ram??

If its over clocks well I would tend to buy another 2 sticks of exactly the same ram..

If your current crosair ram has a week oc, then I would just get cheaper ram that has the same specs.