So I did a quick game with Adventure Creator v1, and tried to upgrade it thru various versions of AGS.
http://babibu.opintanner.fi/ac1toags25.zip
notes:
1. Roger turns into a TV.
2. You cannot walk anymore.
3. The newest version of Ags crashest on an internal error while saving the game (something to do with array size has to be >= 1, in internals of the game).
Usability of this information may be close to zero, but I had to try ;)
Seems that true upgrading would require serious amounts of fixing by hand (graphical scripts and the like).
And walls, etc.
In fact I'm amazed that a V1 game can still be converted to V2.5.
Maybe it would be better if you take a look at CHANGES.TXT, find out the versions with more critcal updates, and try to upgrade them using these versions step-by-step, which will hopefully yield better results.
Hehe, interesting. But seriously, I have to admit that I don't plan on spending any time fixing this :P