Welcome to the forum, Hobbs. The first question I would ask is if you've recently had a succesful installation of anything from other sources. If you have, then what I'm about to say may be off base. But, if you haven't:
It looks to me from that one example that Windows is having trouble fetching files that it has put in a temporary folder for the installation, which, as you may be aware, is a standard way Windows installs a lot of things: unpack to a temp folder and then do the install from there. Even if you've specified another place to unpack the files, Vista deflects some unpacked files and some installed files to places like the AppData and ProgramData folders. No sense making it simple if you're Microsoft! To me, especially if you have problems installing programs from other sources, this would indicate some damage - hopefully minor - on your system. Maybe some damage to your .Net Framework, the basic underlying architecture that Vista runs on. It correlates to the old Visual Basic runtime libraries, (some of which are incorporated into the new system for backwards compatibility) if you've heard of them.
First, are you running the installs as Administrator (or running from your administrator accounts)? Under Vista, some of the GOTDs need to be installed (and sometimes run) that way. If you're not familiar with that option, when you RIGHT click on the programs you see "Run as Administrator" (obviously, if you're not already in your admin account). Select that, and it will run. It should trip your User Account Control, unless it's turned off, to get you're permission to run as adminstrator. However, some of the GOTDs do this automatically. You can tell because the icon will have the standard Windows 4 color security shield icon grafted on in the lower right hand corner, though it's tiny. Those should already trip your UAC. If you've had trouble installing programs that already run as adminstrator, then this tip won't help.
Have you done error checking recently? If not, I'd do that, including checking for bad sectors, especially if your hard disk has got some mileage on it. I'd also run System File Checker. I don't know if you've heard of that. It's an old tool from the Win 98 days that Microsoft has hidden on you're system so the IT pros can you use it, because, after all, the rest of us are too stupid in their eyes. It can find and fix damaged system files. If you're using the new start menu, type SFC into the start search box. If you're using the classic menu, type it into the Run command box. SFC often can't repair everything, especially since Vista has so many more security restrictions (which, unfortunately can get messed up and may be related to your problem), but it will at least give you a log to read so you could find out if anything's still bad and even try to replace the bad files by hand. The bad news is: you need a workaround to read the log and because of the security restrictions, replacing the files by hand is a hassle. Been there, done that. But, that would be down the road, anyway. I'd run both of those tools, first and see if that fixes the problem.
Also, technically, a System Restore (back to an earlier date) might fix any damage, but I think that would be way premature. No reason to use a System Restore if you haven't even verified that you're machine has any damaged files. There wouldn't even be any way to decide on how far back to restore the settings.
Good luck and let us know what you figure out. :)