Magento

I sort of need a calendar on my checkout page.  I was looking at the gift message code and figure I could splice something in the same way.  The problem is that I’m having trouble following where everything goes.  Can someone point me to either a good php reference or a good php editor.  I can follow the logic but the code is fragmented (just another way to say modular) so I’m having trouble finding just where everything is.

Munchy Monster