Am I missing something on the additional installs of Wow?

I have been running 4 instances out of the same WoW folder and wanted to try installing Wow again under Wow1 folder(or something like that). Upon inserting the install disk it prompts me saying "I already have that software installed " Dumb question, but how do i get around this ? I only experience lag when portals/ hearthing , so forth. My system is fairly powerful and think that the lag is coming from running all out of the same folder.

E8400, 4 Gigs ram,4 HD's(Raid 0+1), single 8800 gt512 atm. Vista Ultimate 32 bit.

Sorry for the newb question , but thought someone here would know the quickest solution.

Nazzzcar

I just copied my WoW folder to WoW1, WoW2, etc. and then made new shortcuts

With your setup, you might do better with Vista 64. I used XP64 with similar hardware and 8 Gigs RAM and was able to get 5 sessions all running at least 50 FPS. The one thing that you really need to do is to create a separate client directory for each session. Even with 10k RPM uber fast drives, you will fair much better than a shared directory arrangement.