There isn't a root location in XDCC, but if you're talking about fserv....
If you have your files in a location such as c:\fileserver\ and subfolders in there, then that's your root location.
If you really are talking about XDCC, you're supposed to put individual files in there... just browser for them.
And as for sending files, if you can't send any files, then it is a firewall or router problem. For router problems, go to
http://www.portforward.com/ for help. If you are at a college or work or somewhere else that has its own firewall that you can't access, then you're stuck... the workaround is to use Reverse DCC, which will only allow some people to connect and download from it. It's better than nothing, though.
For more help with firewalls/routers, click the firewall/router stickey thread at the top of this forum.
You can find me at #Invision on irc.irchighway.net or #OldGames on irc.undernet.org if you need me for anything.