I started with the key tag punch andI think I did pretty well.
Instructions as follows:
1) Mark with pencil the 1.75 inch length where you want the window.
2) Then punche an oval inside the markings on either end
3) use little scissors to cut across at the top and bottom to connect the 2 oval shapes to make the key tag negative.
And voila, you have a nice key tag shaped window.
And just in case you haven't seen any great punch art using it, here's the link to my Pinterest board where I've collect a few ideas I've found on the web: http://pinterest.com/punchcrazy/su-key-tag/
Now I have to go and work on some recipes for the cute Valentine cards I've made and wish to share over the next couple of weeks (so far I have 8 punch art cards and have many more ideas floating around in my head).