Should be pretty simple. Assuming that your TIvo is already configured to record from the Aux Scart socket (eg from Sky or Freeview), just plug the VCR or Sky+ into the Aux socket, and start a manual recording on Tivo on any channel (eg 101 i on Sky, 1 if on Freeview) for the correct duration.
That will cause it to copy whatever is coming into the Aux socket - so just press play on the VCR or Sky+, and Tivo will record it!
That will cause it to copy whatever is coming into the Aux socket - so just press play on the VCR or Sky+, and Tivo will record it!