Yes it can be used on a different computer, Microsoft may have a license for that computer it was bundled with, but there are loopholes. For example, if you buy a new motherboard or hard drive, you may qaulify for a new OEM copy of Windows from the vendor that you bought the computer parts from. A local vendor, sells bad SCSI drives for $1USD each and then can sell you an OEM copy of Windows with it at the OEM bundled price. That way we can get a legal copy of Windows without buying new hardware. Nowhere does the OEM License say that the hardware sold to qualify for the OEM license has to work.

Plus if you use parts of the older system in the new one, technically, it could be the same system as before, just with new parts added.

So yeah, you could use that OEM copy of Windows somewhere else. Just don't tell anyone about it, keep your CD-Key and Serial Number to youself, and be happy. Or just get Linux and WINE instead. ;)