Nero OEM versions come in several variants which differ in which of the programs in the full suite that are included. The programs that are included should be the same regardless of whether you're using an OEM or Premium version, but OEM versions are sometimes tied to a specific drive so that they don't work if you remove that drive from your system.
Even if you have an OEM version installed, you should be able to upgrade whatever programs are included by downloading the lates update(s) from Nero's website.
If you have a Nero Premium serial number, you can enter that serial number in SmartStart to enable whatever functionality is missing when using only the OEM serial number. At least that's how it works with Nero 6, but I can't guarantee that Nero 7 behaves in the same way.