ROM n' Apps
If you are vaguely familiar with Java, you should not have much problem with application development for android. A great book to assist in learning the android app way is
here.
There is also an app inventor application that google labs is hosting. Try it
here. You can create apps here, but if you need to get down and dirty, you will need to know Java.
I have the basic understanding of ROM's but no time to spend learning to create them, so I will leave that answer for someone else with more knowledge on the subject.