Changing Techs.

I remember changing a couple of techs when I played civII so we couldn't advance into the modern era, is it possible to do this with civIVbts or does it require a lot of computer knowledge as in civII it was just wordpad?

Thanks.

Not with the vanilla version of BTS. However, there are unlimited possibilities with modding. You should check out the Creation and Customization forum (Mod forum). Many modpacks have been created that change the game significantly. Some mods do focus on specific eras like ancient, classical or medieval.

You might check out Rhye's mod and modmods. It's actually delivered with BTS, but has been updated. You can get the patch here. Although you can attempt to play any civ in Rhye's through modern times, each civ comes with Unique Historical Victory conditions that can be finished much earlier.

Another thing to consider though with the base game is that, as you get better, you can win the game much earlier than modern era, especially with certain victories like Domination, Conquest or AP.

I don't think this will be all that difficult, changing the cost of any building to -1 makes it unobtainable so I think changing techs cost to -1 would do the same, so modding to prevent going past a certain point would just require changing selected tech costs.
Alternatively you could alter tech prerequisites of any tech you want unavailable to future tech or another impossible tech, doing either of these from top to bottom of the tech tree would be all it needs to block further progress (4-5 techs).

You should copy the XML folders and create a mod folder before trying this as you don't want to change core files. Like Lymond, I also advise going to the creation and customisation forum first, if only to find the tutorial on modding XMLs.