A portable program offers some advantages:
Not all kind of software can be written in a portable way, but "normal" programs can, and usually I try to do so because I prefer this approach.
If you want to install a portable program on your PC, the more sensible way is to copy it inside a directory outside the traditional C:\Program Files\ path.
This because, starting with Windows Vista, a program installed there is supposed to not write inside its directory and to keep its privata data elsewhere (%APPDATA%).
If you put a portable program there anyway, and it tries to write inside its own dir, the OS permissions will stop it causing errors or other problems.
If you really want there are ways to install a portable program there but the best thing to do is to create a new tree in the file system for your portable progams.
For example, on my PC I have a C:\Portables under which I keep all the portable stuff, with each program inside its own dir.
I suggest you to do something like that.