Simply Maya User Community - How create file-open attribute?

I have written a plugin that allows objects to be scattered on surface. But I cant find the set of attributes. I need to create an attribute that looks in Maya Attribute Editor like this:
http://img379.imageshack.us/img379/6311/fopenfj0.jpg
as well as other attribute that looks in Maya Attribute Editor like this:
http://img70.imageshack.us/img70/4863/objectfc9.jpg
Simple MFnTypedAttribute with the MFnData:: kString

Code:

MFnTypedAttribute strAttr;

mobjString = strAttr.create("ScatterFileName", "sfn", MFnData:: kString);

looks like
http://img292.imageshack.us/img292/6538/simplevf4.jpg
I am not very satisfied.
How can I create required attribute?