Hello, I am trying to install the Conversion Mod which adds a lot of stuff, so I'd love to have it, but after the dev logos, it just crashes. I have no idea how to fix this. I've tried reinstalling, and it didn't work. If you could help me, that'd be great. Thanks!

Use offline version.
Make sure to install some un-official updates.

GOG do not have proper 1.1 version. They rollback offline to 1.1 - but they actually rollback it to 1.0 with 1.1 exe. nstall that un-official patch that have 1.1 include.
If you cant find that - google it on torrents old 2.0.0.5 GOG build or "legacy WinXP compatible version" as GOG labeled it.