Programs won't let me install on different partition

I've tried installing Flash MX on my E partition (144 GB) but it won't let me when I'm installing it. When the window says install here "C:\Program Files\..." I type in E:\FlashMX and then hit next and after I do that it says "there is not enough room on the highlighted partition, please choose another partition to beinstalled on. I see my C partition (4.5 GB) and my E partition. The C partition is the one highlighted and it won't let me select the E partition. I've tryed restarting my computer and installing programs. I get the same thing. Although like 3 minutes before I tried installing Flash I installed "Vista Inspirat" without a hitch. BTW, only have around 100 megs free on the C partition.

u think it might need to put some files on the C:/ drive regardless?