Exactly the same as the retail version [Original Equipment Manufacturer]is what OEM stands for, and in general is hardware/software sold to system builders/suppliers for distribution with a new PC.
Most suppliers will sell you an OEM version of software if you buy a small hardware item at the same time. Many will sell the software without these restrictions applied.
In general, buy the OEM version and save yourself a fair bit of money. The main concern is that the supplier is responsible and not the manufacturer for help with any setting up of hardware/software. This will in most cases not present any problems, especially with software. j.