As I understand it, there are only a few digital OTA boxes that the Series 1 knows the codes for.
People have come up with hacks that would insert a new code set for the Series 1 to use, but supposedly the next time the TiVo phones home, the software can be changed back to how it was before.
Someone did do a thread recently about what boxes the Series 1 can already control...
I'll try to find it for you.
I use an Echostar DTV Pal, since that uses the Dish Network IR commands, and I just lie to the TiVo and claim I'm using a Dish box but remove all but locals from my channels list.