-Click on Start - Run... and type the following :
regsvr32 "C:\Program Files\UGS\NX 5.0\UGII\ugpropext.dll"
-You'll see that the dll has been registered successfully.
-Log off and logon again (or just end the 'explorer.exe' task and create a new one if you're as lazy as me)
I've tried this with NX4.0.4 and NX5.0.4 successfully.