Most programs not only install key files to the local drive:\program files directory, but also to other directories, create registry keys, and latch onto key files that already exist on your system. Thus, only programs created for "removable use," such as Firefox Portable, can be run entirely from a flash drive. While you should be able to redirect the installer to the flash drive as opposed to your hard drive, it won't run solely from the flash drive. Also, Yahoo IM (from the flash drive) won't run on another computer unless you go through the installation there too so that the other computers have the files required to run the program.
Hope this helps,
John
I have successfyully got an internet browser to load onto a flash drive and am up and running my web browsing now from a flash drive. No problems getting yahoo mail to be accessed from this flash drive. However, when I tried to load Yahoo Messenger onto the flash drive , it kept wanting to put it onto my normal hard drive on the PC. I can't figure out a way to direct the Messenger software download onto the flash drive. Any suggestions.
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic