Question re Precision M4500--32 bit to 64 bit conversion

I have seen some refurbished Precision M4500's in the Dell Outlet store at attractive prices. However, they are all running 32-bit Windows 7. I'm prepared to do a clean install of 64-bit Win7 if I buy one of these, but I'm wondering if (a) I have to buy a separate 64-bit version OEM disc somewhere on the internet, or (b) could I do a clean install of 64-bit from the supposedly 32-bit installation disk that comes with the M4500 or (c) if I could simply use a Win7 disc that came with one of my other machines, but use the serial number that came with the M4500.



Any thoughts about how to do this?



For that matter, any thoughts about refurb Dells?