Looking for a Code Management System. Advice needed.

Hello,

I develop an application from a year now. It is written in C and the whole project has around 20 files (*.c *.h). I continuosly make changes and I maintain by hand all source changes in a directory, where aech folder is a version of the sources. Now this is a very inneffective way to maintain source code changes.

Now I am thinking in using a Source Control Versioning software. I have been reading in the web here and there and have found there a lot of tools, many of them even requiering a web server..... so, because I have ended crazy of so many readings, I would like to ask for advice in what tool to use.

So, my needs are the following,
- Maintain a little application of 20 source files.
- I am the only programmer. There is no need of access control.
- I encourage to have a Gui and simple to use. Maybe this is the main point for me. Windows OS
- And finaly, if possible, to let me have the repository database in a pen drive to allow me to write code anywhere.

I would appreciate any help in the area.
Thanks a lot.
Fermin