If you are running a 32-bit version of XP, Vista or even Windows 7 (I keep hoping for a 64-bit version), you can give Portable Ubuntu a try.  Portable Ubuntu will give you the top bar (you’ll recognize it if you have ever used ubuntu…) right in your windows environment.

It is very easy to use / run:

1. Download it from here
2. Extract it (execute the file you downloaded)
3. Execute the “run_portable_ubuntu.bat” batch file in the directory you extracted it to. The initial loading takes some time (up to 30/40 seconds) but once it’s running it runs smooth and fast.

Basically this is a portable virtual machine that runs in seamless mode, meaning you can run both the host and the guest side by side.

This makes this Ubuntu a great portable OS to take with you on your disk on key, external HDD. After installing updates and adding a few programs, the size of the entire folder is still less than 2 GB.