VBA - Excel Addins

I have built up an application using VBA in excel. I am trying to make an addin out of it.
Have following problems:
1.)How do I access the orginal worksheet from which I am installing an Addin....coz as soon as I Install it. the focus is set on the addin. And so even when I write Thisworkbook.<Properties,methods> in the addin.....it does not seem to get affected in the original workbook. Is it so that when I install an addin, The active workbook becomes that of the addin workbook....then How Do I reference the code in the addin that make changes in the original worksheet and not the addin worksheet(Which is invisible)....

Oopssss.....Can anyone please suggest me some good books/Sites where I can get some info on Addins....or some suitable examples that will make some of my concepts clear.