Strange but true.
I was happily using hijack_hl2, then steam updated half-life 2, and the wedge broke.
I was back to using my precious DVD for a week. Then just now, I tried hijack_hl2 agan, with no DVD and it worked!
AFAIK, nothing in the game has been updated sence it broke, so It seems that there is something more complicated going on!
Acarphinus