yep thats possible. First you install gp4 a first time. Then with norton partition manager can you tempory remove the drive letters from a partition. So you remove the drive letter of the partition you installed gp4 on. You install gp again on a different location and then you refer the drive letter back to the partition of your first install.
you can also simply copy your gp4 installation to another folder. you will have to start it with the exe in that folder cause there are no registry entries for the copied gp4 but it works
when i played gp4 last, i had at least 8 different installations at one time,all using the "copy paste" the gp4 main folder technique and they all worked fine..