virtualbox.org

I installed winxp as guest on a linux host, and I would like to (dynamically) access the files of the guest os.

The virtualbox shared folders mechanism work only in the other way: host -> guest.

How can I do that?

Maybe through samba?

any suggestion is welcome

Samba is the way you need to go. You don't need the server, only the client part. Make sure that you have set your VM to use Host Interface, else it won't be accessible. Then follow any howto to access Windows shares from a Linux machine.