Design Patterns discussion

[patterns AT celticblues.com]

Let's I am writing some code that will read two or more different file  
types.  Assume that I will have a BaseFile class, and two subclasses.   
With the load of specific file contents performed in the Load method.

BaseFile
{
.
.
.
   virtual bool Load() = 0;
.
.
.
};

FileTypeOne: public BaseFile
{
.
.
.
   bool Load();
.
.
.

};

FileTypeTwo: public BaseFile
{
.
.
.
   bool Load();
.
.
.

};


What I need, is a way to create a new file object type without  
necessarily knowing which type of file is going to be read.  For  
example, if given the name of the file to be read, I pass it to some  
function/object and it will return a ptr to a new correct type of  
object.

BaseFile *newFile = CreateFile(filename)

Seems like this may be a job for a factory or factory method but I am  
not sure.  What pattern would best suit this functionality?

To make matters more confusing, this is for a real time simulation, so  
it needs to be lean and mean, and preferrably simple to implement and  
update as new file types are defined.

Thanks,
Ed