Raj,
For plugins, I recommend downloading Beat's API documentation
www.joomlapolis.com/component/option,com_docman/task,doc_download/gid,16/Itemid,36/
and then looking through another plugin that you like... phpBB connector, simpleboard plugin, etc.
For php, I bought a copy of this book
www.amazon.com/gp/product/0672326728/ref=pd_bxgy_text_b/102-3954820-3960108?%5Fencoding=UTF8
If you are pretty familiar with VB and programming in general (including Object Oriented Programing) then the crash course in PHP should be pretty good... worked for me anyway. Also remember 'Google' is your friend... there are many websites which offer php references and tips/tricks... Zend, php.net, etc..
Code editors... Zend Studio is good (but not free), Crimson Editor is a good 'programmers text editor' (but not an IDE)... I have played around a bit with phpDesigner (not sure exact name) but it worked on one machine and not another... first glance was ok... Between Zend and Crimson Editor that covers the bases for me... I think some HTML editors like Dreamweaver have some limited php coding... they are excellent for html though...
Hope this helps get you started...
Greg