Nope, there is no way of being sure as such, I've never heard of M745A yet, so I think it might have been manufactured separately for dell, and only dell laptops have them. The best way to find out is to call them. Perhaps if you could provide us with the model number and all that? Even so, you never know, just like Apple shipped those mac books with different processors then that were ordered.

If you don't get a 400Mhz FSB then you can always over clock (and yes I do believe it is possible to mod the processor on a dell inspiron laptop so that it has a 533Mhz)