how to select an item from a select box and display it on a textbox on the same page using ajax?

Answer 1

Not particularly hard. Any javascript reference will cover this.

Add an event handler to the onchange event of the select list.

Assign the value of the textbox to be:

this.options[this.selectedIndex].value

Should do the trick for you. "Ajax" is for the most part, just a fancy name for javascript, and a bit of googling, and a decent understanding of the DOM, and you'll be able to do this sort of thing fairly easily.