Is it possible to run windows 7 apps on windows 8 ?
Yes, so long as it's not ARM (and hence running Windows RT).
.Is there an easy means to click on a file and tell it to install it as if it was running on windows 7?
Yes, but only for desktop apps. It doesn't work for the new-style Store apps - the latter can only be installed from the Store (though there are some options for sideloading if you get a free-but-registration-required developer license).
. I installed a virtual machine in windows 7, only to find that my video card didn't have an XP driver other than the default windows one
This doesn't make sense. Your physical video card is not exposed directly to the VM, the VM gets some sort of emulated one, the performance of which depends on which VM software you are using.
I really like the people at Good Old Games that figured out a way to make a large selection games run on a modern
Most of GOG stuff is just the original game packaged together with DOSBox. You can do it yourself for many other titles if you can obtain the original binaries.