Thanks, but I figured it out. There's a hidden folder in "Program Files" named "InstallShield Installation Information" and even though I uninstalled the program, the folder containing the information for WinPOET was still in there that is why it kept saying that it was "unable to find installation directory". I deleted the folder and I could reinstall the program again.
Unfortunately, I don't know why (I have Win 2000 Pro) but the OS will not recognize the adapter that the software installed (iVasion). I guess that was for the better because I proceeded to get myself a router and connect my dsl through PPPOE. It's easier and no more unnecessary software.