SMPlayer Portable Edition is a special version of SMPlayer (for Windows)
which tries to not write anything outside from the directory where it is
installed, so it can be used from external devices like pendrives. 

You can get a package from here: 
https://sourceforge.net/project/showfiles.php?group_id=185512&package_id=284416

To install it, just uncompress it wherever you want. To run it just
double click on smplayer.exe.

The package includes:

* SMPlayer (portable version)
* A MPlayer build
* Translations and icon themes

What are the differences with the normal SMPlayer?

* By default it will save the ini files in the smplayer's folder.
* It won't try to create the smplayer home directory or the screenshot
  directory (C:\Documents and Settings\User\.smplayer\...)
* It won't write anything in the Windows registry (for that reason the
  file associations are not available in this version)
* The screenshot option is disabled by default.

How to know if it's really the portable version?

Go to Help -> About SMPlayer, it should say something like this: 
"Version: 0.6.2 (Portable Edition)"