You have to be rooted and you have to have the kernel module for cifs support. if you have froyo, you also will need slow-work.ko kernel module as well.
Once you have those, you can use (shameless plug) Mount Manager, it can handle loading the modules for you automatically and lots of features available for auto mounting when connecting to wifi, and other stuff. It is a lot like Cifs Manager, but has a more robust system for loading the modules, and supports multiple modules and has support for being a plugin for locale/tasker (paid version).