memory - Buying more RAM

I have 2 memory sticks, each 1GB, DDR2 operating at 667 mhz. I'm looking to buy 2 GB more, and have two questions:

1. Should I buy 2 pairs of 1 GB, or 1 stick of 2 GB? Does it make a difference nowadays?


2. Should I buy 800 mhz or stick with 667 for better compatability?

Edit - given that 800 mhz costs the same as 667, will 800 perform worse than 667? If not, I might as well buy the 800.

Answer

If your motherboard supports (and most likely it does) dual channel RAM you should buy 2x1 GB modules.

As for buying 800 MHz - if you combine different speed modules they will operate at the speed of slowest ones. So if you don't intend to change old RAM but only add 2 GB, buy 667 MHz if you get it for cheaper.