well, aight.
As far as making your own: win media center seems the best so far (not saying a lot, tho) Also, Rad7500 with an RF-remote is a must. You are looking at $500 min.
Also, you have to think about which device is going to change the channels: sat receiver or the ATI tuner. If you must use the receiver then all the guide programming on the PC will be useless.
Again, a combined Dish/Tivo receiver might be a good way. Altetnatively, certain Echostar models can work with Tivo: from
here
Listed below are models that have been tested and are compatible with TiVo DVRs. You'll need to refer to the owner's manual of your satellite receiver's to find a model number.
2300
2700
3000
3700
3800
4700
5000 (most recent version)
7100
The fee can likely be reduced to $5 if you subscribe to both TiVo and Dish.
(edit) btw, in certain areas the cable companies are rolling out PVR service. For $10/mo you get an 80GB PVR, no hardware costs! I've had it since September and been loving it! All digital channels, one remote, works very well.