@OP
this is how it works
SDRAM (hardly ever seen today) - 168 Pins in 3 sections (2 keys)
DDR SDRAM - 184 Pins in 2 sections (1 key)
DDR2/3 SDRAM - 240 Pins in 2 sections (1 key)
Because of the different numbers of pins, only DDR Ram will work in a DDR slot etc.
You need to look up your exact model, find out what type of memory it uses, and it's maximum speed (e.g. DDR2 667) and find memory that conforms to it. Alternatively, you could just buy an upgrade kit specifically designed for that model. In the future, i suggest you find out exactly what your machine takes before getting touchy feely with the buy buttons.