Assuming you're on Windows...hold down the Shift key as you start iTunes; you'll be prompted to create a new library or locate an existing library. Since iTunes really enjoys naming folders after itself, the folder you select to house a new Library will have another folder created inside it, named something like "iTunes 1"; your new Library will be in there. (Along with a new iTunes Music folder; the "iTunes Music folder location" pref will be automatically set to that new iTunes Music folder. Of course, you can change it again to whatever you want.)
To just move your existing Library files, use the Choose Existing option (after moving your library files, of course ;-) Might be a good time to do a deep cleaning of your xml file...it accumulates lottsa junk. To be rid of the cruft, move only the "iTunes Library.itl" to the new location; a new (clean) xml file will automatically be generated.