Any side-effects to running 2 different brands of RAM?

I currently only have 256 MB of Kingston PC3200 RAM in my system. I'd like to upgrade to 512 MB in the near future and would like to possibly get a better quality stick.

Is there any reason that running 2 different brands of RAM would present a problem?

It looks by the model number of your board that it is a Sis 648 chipset. These are single channel, and as such tolerate a fair degree of mismatch. Dual channel boards detest mismatch entirely.

Bear in mind that multiple sticks of ram in single channel machines typically hurts the memory overclock potential, and in the best case your new limits will be defined by the poorer of the two sticks. But it should work fairly well in your case if you aren't trying to run the ram above 400MHz.