I had this game on original CD and I got the original guide etc. but one thing that has eluded me was the different type of trucks on the purchase screen.

There are 3 other types but you cannot select them and I never worked out why or if you could, I assume you could.

Anyway if any one knows anymore about it let me know :p

You can't, and even if you could it would merely be an aesthetic choice . Maybe they originally planned to have different types of trucks, with different attributes, but it was never implemented in the final version.

from what i've seen from the xtx files there were a lot of things that were never implemented. but that's always the way of gaming companies