It sure is. Stick with the 2x1GB for now, and if you wanna upgrade get another 2x1gb kit of the same matched ram. And make sure your gonna be running a 64-bit operating system so it will support 4GB
Or if you wanna sell that RAM and get something new that could possibly overclock better, you can get a 4x1GB kit of Crucial Ballistix DDR2-800 for around $120.00 USD total which is a steal!
To start off with, id try 5-5-5-15 timings, 2.15 voltage, and DDR2-1000 MHZ frequency. If that boots up with no problems, download this right here, and burn the .ISO file to a disk
http://www.memtest86.com/
Then you can go into bios, and go to boot menu, and change the boot device priority to your CD-ROM drive and boot with the disk and it will run a memory diagnostic test to check and see if your memory overclock is stable or not. Once you get that up and running, let it run for atleast 2-3 hours and if you get no errors, then that OC is stable. If you get errors, try upping the voltage just a notch and try again
Just like overclocking the CPU, is time consuming but worth it

__________________