Hi Tousi,
Absolutely yes!!! I have WAS ND V6.1, V7, V8 and V8.5 in the same box.
You can install without problems you only need to install in other directory (f.e WebSphere/AppServer/V7 and /V85)
If you create a server you only need to take in mind to use differents ports to avoid port conflicts.
Hope this helps. Tell us if you need more support
Regards