Windows 7 - Installing and updating software under 7

I have two machines upgraded to Win 7 from Vista.
On both machines there have been problems installing and particularly upgrading odd bits of software - but not neccessarily the same on both machines. So for example, on one machine Java works fine. On the other Firefox says that a java plugin needs to be installed, but then it won't install.
They all seem to be access and permissions issues - and I suspect that the software installer wants to use some folders that Win 7 thinks it shouldn't be accessing. For example the Microsoft uninstaller wouldn't install because it needed access to a folder in the c:\users\username\.... path.
But beyond that I'm mystified.
Any ideas?

I'm not to operating system savy. I'd love to get rid of "Bing", but don't know how, I just go to another browser, because I'don't plan to use it at all.

tbernstein, I just love the dog!