PEM is a program I wrote to handle portable programs. It essentially acts as a portable file association manager. You pick what program you want to open a certain file type, then pass that file as an argument to PEM, and it will launch that file using the program you want.
The nicest part about it is a context menu option that is very easily installed and removed. It adds an option to every file to open it with PEM, whic essentially makes it as easy as double clicking the file.
Another nice part about PEM is that it can autodetect the drive letter, so you can really take it anywhere. Check it out here:http://freewarewire.blogspot.com/2009/06/pem-pure-enigmatic-magic.html
I included the source too.