Have you looked at your user guide? If you don't have it on your hard drive, you can download it from Dell's web site. There're also hardware forums on Dell's web site where you can ask questions. I've never heard of Crucial being wrong about these things, but then there's always a first time for everything.
I have an original XPS700 with E6700 core duo 2.66ghz running Win7 PRO 64bit OS and the 1.4.1 bios. Has anyone ever put 8 Gb of ram in one of these machines? Crucial tried to tell me it would only run 4 Gb and book says 8b. I am puzzled.