There are no special actions that wspbuilder needs to take to have multiple functions in one solution package. All you have to do is create a new folder for each function in the 12 \ TEMPLATE \ FEATURES folder inside your solution in Visual Studio and put the corresponding feature.xml file in this folder. For example, you might have:
12 \ TEMPLATE \ FEATURES \ FancyFeature \ feature.xml 12 \ TEMPLATE \ FEATURES \ ReallyCoolFeature \ feature.xml
... etc.
wspbuilder 12- wsp manifest.xml. "TEMPLATE", IMAGES, LAYOUTS ..: , 12 .
12 visual studio, manifest.xml.