I have found how to "debug" the 320'000'000 maximum population stop
Is it the right place to post that message ? I'm not sure, but I didn't know where to put it.

It works for the civ2 multiplayer french version, with the latest patch. It should be the same for the english one.

1) make a copy of civ2.exe (just in case)
2) Hex edit the civ2.exe
3) Find the second pattern of "007d", it should be followed by "00". (it is 0003633c on Hex Workshop 3.1, a freeware)
4) Replace it by a higher number, for example "ffffff" and your population count will go much higher than 320'000'000.

I would like to know if it works for someone else too. (my computer : 450mhz and 192mb of ram)

I don't know why the programmers did stop here. Maybe that your population affects how the AI values your situation and too high a number can alter the negocation process. But anyway, if you have that kind of population, there is no need to negociate with Caesar anymore.

The same method of research could perhaps be used to break the 30'000 gold limits.
It is 3075 in hexa and appears about 25 times in the prog. Should be easy to test.

I am much less optimistic for the 255 cities barrier. I don't even want to know how many times FF appears in the prog, and probably that it wouldn't work anyway, each cities requiring a lot of informations. It's not just a number to change in this case. But if anyone wants to give about one year of his life changing patiently all the ff00 in ff01 to see the ones that rules the 255 techs and the 255 cities, he has all my sympathy.

So one can guess that the maximum population should be 255x10'810'000(city size 46 : plains and 4 oasis/wheat) = 2'756'560'000 citizens. But maybe that you cannot have a map able to support 255 4-resources cities, so it should be a trifle less. Or more if that legendary 5 resources within a city radius really exists (please see my topic in the civ2-help section).

Anyway, I am quite happy with my little discovery.

Just to make it clear.
As for now, I've just suppressed the 320'000'000 population limit.
I think it could be possible to do the same with the 30'000 gold limit. I'm not sure. I shall try it this week-end (far far away).

Just the time perhaps for someone to tell me whether it would be legal or not to give (for free of course) a new version (let's call it a patch) of the main .exe programm of a game.