Do you want to image with the DSI as well as guide?
I asked a similar question here recently. Seems it is possible, but haven't tried it.
If not, you'll need a guide scope as well as your imaging scope, or a camera that is capable of imaging and guiding at the same time. Think they have 2 chips on them, one for each, but not sure about that.
Free guiding software:
PHD Guiding
Guidemaster
EQAlign 2