@Gav
Right... quickest way to do this is:
1. Press right amiga and e at the same time to bring up the execute command box.
2. in it type "ed s:user-startup". Your user-startup will load up in ed.
3. At the end of the user-startup on a new line add: "assign Duke3D: misc:duke3dshare/"
4. once thats done save your user-startup. quickest way to do this is press the esc key then press x followed by return. That will save and exit ed.. very handy. If not you can do it under the right mouse button menu.
5. thats it... to activate the assign a reboot will be needed.
You can however do a temp assign by typing in the assign line above directly into the execute command box.