I curently have a modal window for login using simple modal login,I have to have another modal window within the same page whenever a link is clicked on to produce account,which may also be a modal window.How do i have multiple modal home windows using simple modal Login wordpress plugin ?What files should i change to be able to make that happen? please advise.

You could have as numerous modals around the page as you desire only ever one at anyone time.

$("#element-one").modal({options});
$("#element-two").modal({options});

Place the above code in the same location because the other JS around the page and set your html link in wherever you would like it to show up on your website.

<a href="#" id="element-two">Link to activate 2nd Simple Modal</a>

The wordpress plugin uses the jQuery simple modal wordpress plugin so that you can examine the documentation there for additional help:

http://www.ericmmartin.com/projects/simplemodal/