good point about the power supply - ZAP!!!
Say Matt your DSR704 records up to 120hrs? is that by way of an upgrade?
Yeah, I dropped a 160GB in relatively early in my TiVo experience. There is a limit with the current DirecTiVo software that only lets it see 137GB which equals 120 hours +/-. There are more involved hacks that will let you address larger HDs by replacing the kernel. If you are just interested in increasing your capacity, I'd wait for the new software (6.2) that supposed to be pushed out by DirecTV sometime soon. Reports are it has the newer kernel that will allow native support for larger drives and you can get full capacity.
If you feel more adventurous though, feel free to poke around and find out all the other cool hacks available. You can do some pretty cool stuff, especially if you save your original HD as a backup in case you muck something up with the new one.