Sometimes i use yum to download software that didnt come with my distro, and i lose them all when i reinstall my os.

How can i keep a copy of the software along with the dependencies that were downloaded so that i dont have to download every thing all over again.

For example (Vlc + Dependencies + Updates) cost me around 52 Mb. How do i backup those 52 Mb , so that i could get Vlc running later after a fresh install.

Thanks in advance.

Check out your yum.conf file (typically in /etc).

It should have lines like:
cachedir=/var/cache/yum
keepcache=1

The cachedir is where it would put files it had saved which include headers and rpms.
The keepcache if set to 1 tells it to save those files. If it is 0 it does NOT save the files.
You could periodically backup the contents of /var/cache/yum then restore it after a reinstall. You could use "rpm -ivh *.rpm" in that directory after the restore to reinstall all the rpms found there. Since they'll all be in the same rpm install they should resolve all dependencies.

Why are you having to reinstall frequently though?

Thanks for taking time to answer.
I do not reinstall frequently. Sometimes i have to due to some bad experiments.