need to do force uninstall of postgres on windows vista 64

Hi, I'm having some pain getting Postgres 8.3 installed on windows vista 64.

The first time I tried to install it, I was using the .msi version, which eventually hit permissions problems, and when
Iaborted the install, the uninstall did not seem to take. 

Then I tried the .exe version of 8.3, and I ran into the problem documented here relating to Date/Time settings
flip-floppingbetween 64-bit integers and floating point numbers: 

http://www.nabble.com/8.3.7-Windows-Update-Error-td22707651.html

The workaround there is to do a clean install of 8.3, but my original install didn't leave me an uninstaller, so I
decidedto upgrade to 8.4. 

8.4 locked up at first, but then I rebooted my PC and was able to do a complete install and uninstall of 8.4, which, if
nothingelse, convinced me that there's some hope of getting through the install pain. 

Unfortunately, 8.4 does not seem to have PostGIS support yet, which is the major reason I'm trying to go to Postgres in
thefirst place.  So I need to go back to 8.3. 

So, long story short, I need a way to force the uninstall of 8.3.  Has anybody had to do this before?  I can try things
likeforcibly removing the directory, hacking the registry, etc., but I would like to work off of some documentation if
possible.

Thanks,

Steve