You can download free video editing software, then manually search for the start of the advert, mark it, go to the end of the advert and delete it. Also delete any lead-in or run=off video and then save it.
I also convert it to AVI or MPG format at that point. Personally I have found it worthwhile getting Womble MPEG video editor for the task.
The hardest part is getting the original digital recording. I recently bought a Humax HRD-T2-Fox Freeview recorder and found a whole community online at hummy.tv who have customised the firmware on the machine, so it is easy to remove the encryption Freeview put on when it is saved on the box and transfer it to a USB stick, hard drive or over a network