If I wanted to make it where Tanks couldn't capture cities...

[Sizzled Chicken]

...how would I go about doing that?

Also, I want a troop helicopter too, but I can't seem to find one even after scouring the forum.

[The_J]

In UnitInfos.xml, set bNoCapture to 1, then the unit can't capture a city.

Troop helicopter: There's no AI which could handle helicopters transporting troops.

[God-Emperor]

If you set a unit's bNoCapture to 1 then it can not capture a city.

Troop helicopters have been done - it is just a unit set to carry the specific varieties of units (see missile cruisers and aircraft carriers, the relevant tags are iCargo, and SpecialCargo and/or DomainCargo), possibly with a different model (perhaps an Mi-24 Hind or CH-47 Chinook). You should be aware that the AI will not use them, so it the human gets an additional advantage over the AI if you add this sort of thing. Not only that, but no complete general purpose solution to this has been done. There are some partial solutions, including some custom tweaks to the AI in the DLL used by Dune Wars that make it use transports that can move on land but it probably doesn't use them to attack places on the same land mass (I think it is just tweaks to one or more of the UNITAI_*_SEA types, and all that expanse of desert in the mod is actually defined to be ocean).

[Sizzled Chicken]

Thanks bunches.

Well, if they figure out a way to get the AI to use it, let me know.

[AverageDude]

You could also make another helicopter unit in the game and allow it to capture cities. You could think of the helicopter's as transporting infantry to attack the cities, and could even make different types of helicopters fr different units and then scale the strength values. For example, you could have a "tank helicopter" that could have equal strength to a tank and have a "troop copter" that has equal strength of infantry.