1. Create Bootcamp partition
2. Install Windows 7 on Bootcamp volume
3. Install Bootcamp drivers
4. Register W7 using online method
4. Boot back into OSx
5 Install Parallels
6 Create a VM and Select Bootcamp as image
7. Open Parallels Virtual Machine list, Select and Launch your W7 Volume
8. Install Parallels Tools
9. Get on phone and go through the re-registration process (Should only need to do this once as later versions of Parallels have got round the early bug that used to flip the registration process)
10. Install Virus protection software (Minimum MS Defender - free from MS)
11. Start the Windows update process and wait for several hours whilst it completes.
There are 2 versions of Windows OEM. You can not use the OEM version that is branded to a Windows PC such as Dell, HP, etc. You can use the system builder OEM version. The OEM version can be installed only once on a specified computer. This is what you are doing.