I would say try learn using both programs. To learn 3d in 3dsmax or maya it's very good to do tutorials, tutorials teaches you different techinques even if it's boring making a ballon, chess piece or an ugly car, it's all about the techniques, and the more techniques you learn the easier, funnier and faster everything will get. The reason I mention it is because I was also struggeling until I realized making 3d objects is basically all about putting different techniques together. At one point I could even map out in my head how to create a model in 3d by holding it in my hand, every step of it. It's cool and EASY!
although zbrush modeling if not just different, but is actually much harder than 3d modeling in maya or 3d max, modo, blender, etc. these are the basics or 3d programs. zbrush is a sculpting program, like how there are just lighting programs, texture programs and so on. i understand exactly how you feel though im telling you this from a mistake i did in the past, and teachers keep telling me "we told you so" lol
so just have fun with it man soon you'll open the program and model or such;D
Zbrush is sooo cheap compared to Maya, 3DS Max and Mudbox. Maybe you should consider getting Blender if you're low on cash. It's for modelling, posing, rendering and is pretty comfortable to use once you've spent a few hours in it. Also, it's free.