Most keyboards with a USB socket are designed to plug directly into the computer with just a USB cable. The OS will either include a driver or a drive will be downloadable from the keyboard manufacturer's website.
For the keyboard with just the 5-pin DIN sockets a MIDI -> USB interface such as this:
http://www.amazon.com/CREATIVE-EMU-XMIDI-MIDI-Interface/dp/B000JLU26W/
Will allow you to connect the keyboard to the computer.
---john.