Multiple Softwre revisions loading fir NX8...

I have the need to run multiple releases of NX. Today I will be on 7.5 and the next day I will be using NX8. Will this work for me? I downloaded the NX8 Volumill and installed. The software wrote over the 7.5 directory that was there causing the 7.5 not to run. Please note that NX8 now loads to the C:\Program Files\Siemens directory.
 
So in short how can I load for multiple NX releases?