the best way to cripple a civ is to go into the civilization page of the editor and there you can set what units and improvements it builds or doesn't build.
things to do: (this is just off the top of my head as I don't have the editor handy)
set it so they never build workers
set it so they never build science improvements
set their favorite government to despotism
set their hated government to democracy
remove any free tech advances
there may be other things you could do as well, but like I said I don't have the editor handy
====
these will not prevent them from moving into them from getting out of the ancient age but it will severly slow them down.
without workers they cannot build roads, which means they can't link up any of their cities to resources and more importantly from a science perspective they will not get the commerce bonus that a road provides.
without commerce from roads and without libraries and universities the civ should be in real tech trouble.
plus if you set their favored government to despotism they will stay in it and will run the course of the game with a tile penalty and no trade bonus, further stunting their growth.
hope this helps.
note: I think the first person to talk about "crippling" a civilization was paul saunders. he's the first person I saw talk about it at least. Check out his mod, if you want to play an interesting game on earth in which the main european and asian powers vie for domination over the african and american "crippled" civs. it has a lot of really good ideas.
