Its not just the age of the Tivo you have, but also what software release it came with.

AFAIR, if you have a Tivo that you bought *new* with 1.3 or earlier software on it, you should be able to use it as a dumb VCR.

Tivos that came "ex-factory" (new) with 2.0 or later software on them do not have this capability enabled. They require Guide data to work, fullstop.

There was a long post from Tivolutionary on this point in the AVS Forum about 18 months ago on spelling out this in mind-numbing detail.

Of course, he did not explain how they implemented the mechanism, but I've seen the flag in the MFS database during my poking around it.

I have a feeling its in the /Setup MFS Object.

If you really want to know I can find out and let you know.

But if your Tivo came brand new with 2.0 software on it - you're SOL, putting the flag into your MFS database may cause more problems than it solves.
Still if your Tivo never phones home again then Tivo won't be able to find out.

You can work out what release of software was on your Tivo by looking at the Serial number sticker (that you were supposed to stick in the back of the paper manual that came with it).