It does that out of the box. You can run your core/hybrid with all your media and indeed any other files based on it - personally I would recommend keeping them separate, and purchasing yourself a decent NAS device for your network. This allows you to keep your LMCE machine separate from your files so that you can rebuild/reboot/reconfigure with impunity! The wife's laptop, yours and the XBox can all continue to access their files uninterupted.
That being said, if you do want to keep your "file server" along with your media on the LMCE, then that is ready to go out of the box. The /home/public/data folder is exported with SAMBA by default. Under there are Audio, Video, Pictures and Documents folders. You can place all your current documents under the Documents folder. Move your PCs into the LINUXMCE workgroup and they can simply map a drive to that share and access all their files as normal. Also this folder structure is exported using upnp if that is of assistance.