You could check out the Nero Liquid TV product.
It is basically a PC DVR with the TiVo interface. You can get two versions of it, the software alone for $99, or the software plus a Hauppauge tuner, IR blaster/receiver, and custom TiVo remote, for $199 US. The software in either case comes with one year service, which you can re-up every year for $99. I think it uses MPEG2, becasue it suppolsely works for file trasnfers to actual TiVos, which are MPEG2. Generally, a 160GB to 320 GB drive is fine for that.