It doesn't matter if you change the timings in the BIOS just because it says a certain latency timing on the wrapper doesn't mean you're unable to adjust it in the BIOS. On the other hand the voltage capabilities have to be identical to avoid frying the less heat tolerant model.
I don't recall seeing anywhere in my BIOS anywhere to change latency timings. Would you be able to tell me if this RAM would work correctly and not cause any problems with my existing RAM?
What brand MB is it? What BIOS manufacturer? Many "big name vendors" computers have a rather limited BIOS interface, like most all Dell's I've seen. A lower CAS latency can be faster, that is if the MB will let you set it, or it detects that. I've been out of the memory game for years. So I don't know as much on what is currently done. It at least used to be you would set your CAS, and all memory modules would use that speed. So if you had one slower one(higher number), pick the slower speed.
Really though, you have the important things listed. The "DDR2, SDRAM, 240 Pin, 1.8 Volts, 2GB"
If you don't have much control over the memory in the BIOS, there really isn't much need to buy super fancy/expensive ram. Just go with a decent brand, and be done with it.