The OEM disks are exactly the same as the retail disks with 3 exceptions:
1. No support from Microsoft. Telephone support incidents are included in the price of a retail disk.
2. OEM copies are purchased in either 32 or 64 bit flavors. With retail, both 32 and 64 bit disks come in the same box.
3. OEM licenses must remain with the first PC they are installed on. Retail copies can be moved from PC to PC, so long as they are never installed on more than one PC at a time.
You do not have to register anything with Microsoft.