Memory can be one of the most frustrating items to choose from. Usually you know from the start what the CPU and Motherboard will be but selecting the memory can be a real learning experience. There are several specs you need to consider but for the most part the clockspeed and CAS rating are the most important.
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips