Install Adobe CS4 And CS5 Onto Same Machine?

I have had Adobe Premiere Pro CS4 and Adobe After Effects CS4 in the past, but recently upgraded last year both to CS5. I have no problem running AE CS5, but PP CS5 is giving me problems when trying to add transitions. Something about it can't add until I remove some parts of the footage from the A-B roll for I had no handles, which means removing some delicate footage. It will either add at the beginning or the end, but not in between like I need it too. I don't like the new way, so I removed both of them. Really, I had no choice since I had to do a clean install of Windows 7 Ultimate x64.

What I want to know is, can I install both CS4 and CS5 onto the same machine? I know it want take trying to install onto the same drive, I believe; but can it be done by installing CS5 onto the main master hard drive and the CS4 onto a secondary slave hard drive (or vice versa)?

I just want to compare the two to find out why they are so different. Also, my Red Giant Suites, NewBlue FX and Pixelan SpiceMaster Pro, etc. plug-ins don't show up in PP CS5, but they work fine in PP CS4.

As far as the plug-ins, would they be installed into the Common folder rather than the application plug-ins folder?