FF5.0 Install Problem

Today, I upgraded and got my FF5.0 license key. I have been using 4.0. Per the instructions, I downloaded the 5.0 trial. When I try to install it from my downloads folder, I double click the .exe file and nothing happens. I've tried re-downloading 4 times now, tried running the .exe as administrator, tried disabling my anti-virus (in case that was somehow interfering), restarted my computer, and still cannot get the install to begin. I just get the quick "working" symbol, and then nothing.

I've pulled up the Task Manager to make sure there isn't another instance running in the background, and there isn't. I use Windows Vista.

Does anybody have any other suggestions that can help me to just get the program installed? I'm at a loss now, and just want to enter my new license key and proceed!