You can extract them from Maps.BIG and then open them in ZH worldbuilder and replace all the missing texture and objects and then save them and it should work.
If you want the single player campaigns from Generals playable in Zero Hour i am working on a mod that does that, you can download it here:
Generals Campaigns in Zero Hour Mod - Cncmaps Map Editing Forums
The mod imports the missing texture names and speech voices into Zero Hour so that all the maps work. There are 2 versions of the mod, the one at the top of the page in the link is less modified so most of the Generals missions are largely unchaged. The one at the bottom has custom map.inis that change the properties of various units so the missions become quite different from what they were in Generals.
how to import old generals maps into zero hour?
