You need to make sure that the zip file name and the static resource name will be identical. And static res. name can contain only alphanumerics. I usually just cut the version references so later if I upgrade the library it I don't have to search & replace all occurrences. So rename the file to "jquerymobile" and upload it as resource with same name.
The official way
As you can see - URLFOR function takes extra parameter that's a subpath within the zip. Of course you probably won't be displaying images but CSS files - check
The unofficial way
You can see what kind of file path was generated by examining the page source from the example above. In my case it's something like
/resource/1354306153000/jquerymobile/jquery.mobile-1.2.0/images/ajax-loader.gif. The part with strange numbers is some kind of timestamp and funny enough - you can remove it ;)
(the unofficial way means you can use standard
<img> tag if you want).
Regardless which one you choose - there will still be a hardcoded version number. It's your call now. I just repackage the zip with top directory renamed/completely removed so my static resources are really updating seamlessly. If you're afraid that stuff might get broken in future if you'll upload new version - leave it (and probably retain also the versioning in the zip/resource name).