O.E.M versions should work OK, but I would be wary of going 64 bit just yet. There are simply not enough regularly used applications (security etc) that are compatible with 64 bit Vista. I wou;d stay with 32 bit for now.
Later in 2007 we will see a gradual availability of 64 bit versions of common applications.
I am contemplating buying the below item:
I just want to check whether an OEM copy is all I need to install Vista - i.e. are there any other costs involved?