If it's slower than what is required, it likely won't work.  If it's faster, it may work but will downclock - it's impossible to be more definitive without knowing what model you have and what CPU is installed.

Though the system will take PC1066 RAM, it won't run RAM at 1066 MHz with your current CPU - since its FSB is 800 MHz, that's the memory speed cap, even if you install faster RAM.

Thanks for the reply!

I've got an inspiron 1545 with a Core 2 Duo T6500 (2.1 Ghz) 64 bit Win 7.

Thanks.

thanks for the information and quick replies, its much appreciated :emotion-21::emotion-1: