On the Celestron CG5 is an autoguider port. A 6 pin cable needs to go from your PC (e.g. parallel port auto-guider connector from shoestring astronomy) to the mount itself - works a charm.
Try Meade DSI via USB2 -> PC -> freeware PHD program from
www.stark-labs.com, with outputs -> parallel port -> shoestring astronomy adapter -> 6 pin cable -> CG5 mount at the auto-guider port!