You would need to do some heavy duty mods (time consuming) . Depending on what you are meaning by Multi Store Support - as in using the same database with multiple front ends?
You would need to create some intermediary tables, and add fields to several tables signifying what store the data belongs to (there are a number of routes to think about when you undertake such a project as this ) As in how you want that data represented across the stores, and do you want a single log on - so if the user signed up at one site are they automagically enrolled in the new .. or how to store them with out duplication etc.. etc.. It is really not something for a beginner , and if you are asking the question what does it take - well you do not know enough to mess with it.