The switch specifically is a DCE device.
So for a computer to connect it's a straight through connection
So for a 9 pin D connectors.
YOUR PC (DTE) DLINK (DCE)
Pin 2 = TX ---------- RX = Pin 2
Pin 3 = RX ---------- TX = Pin 3
Pin 5 = GND ------- GND = Pin 5
From the CLI manual for the 3800 it requires a VT-100 emulator.
I recommend Putty
http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html
9600, N, 8, 1 serial settings.