If you have seperate user accounts on your computer you can each download your own limewire and itunes...You will both have to be Admins for your accounts though....
Otherwise if your sharing the one limewire and the one itunes, you will have to create seperate playlists and drag and drop your music into each playlist...
You can do this by going to your shared folder outside of limewire, to find this folder you need to select a file from your LW library and hit explore....