Having (gratefully) downloaded my childhood favourite Colonisation i found that i couldn't install the game. I have unzipped all the files and seem to have it all prepared yet when i click on install things go wrong.

I get the menu screen but i only have the option of opening the readme.txt or exiting, there is no install button (a fairly large problem)... if anyone could help with that, that would be excellent!

Have you tried running it in DOSBox?

but its loading up fine... just not giving me the option to install... would that make a difference?

You don't have to install the game. Should be allready installed.

what file?

Install DOSBox if you haven't done so already (Anubis has written an excellent tutorial). Unzip the game into your CDrive folder and run DOSBox. Type "cd colon" (or whatever directory name you chose) and then type "install". Select C:\COLONIZE as the directory you want to install the game to, select your sound settings etc and exit. To play the game you need to type "cd colonize" to change into the right directory and then type "colonize" again to start it.
Once you've installed the game, you can delete the "colon" folder again, obviously.

If you want to simulate a disk installation in DOSBox I strongly suggest you to install it from the a:\ path. All computers back in the day had floppy configured to a:\ for installation so some hard coded games may require that you install from either a:\ or b:\ without exception.