You can use directional drilling or, based upon local regs, put a culvert in the creek at the point of crossing,backfill it and use a backhoe to dig under the creek. Run your lines, clean up and pull the culvert. I would recommend against making the crossing with PVC. Use some stout HDPE and, since the big expense will be the labor, run more than one line so that you have a spare in the event that something happens to the primary line.