so it seems to be a windows installer issue? good find. here's the solution for those who can't get to that thread because of firewall issues:
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Nigel Molesworth

Installing Photoshop CS3 on Vista PC [SOLUTION]

I've just spent TWO DAYS trying to install PS3 on my PC. The install seemed to work OK, but when it finished only some of the components were installed. I read all the Adobe KB articles, but still no luck. Finally, I've come up with a solution that worked for me. This may be of interest to Photoshop users...

1] Install Microsoft Windows Installer CleanUp Utility from
<http://support.microsoft.com/kb/290301>

[2] Run the CS3Clean script from
<http://www.adobe.com/support/contact/cs3clean.html>.

Select the [undocumented] level 4 cleanup. This removes ALL Adobe
applications.

[3] Turn on User Account Control - may not be necessary, but it is for Adobe Reader!

[4] Copy the Adobe CS3 folder to your HD, right-click Setup and select Run As Administrator