Survey Form with Skipping and Validation

Hi, 
im developing a survey form, its a collection of lots and lots of textboxes, Dropdownlists ,some radiobuttons and ofcourse labels for labeling purposes like Q1 for question 1 and so on.
Skipping:

the survey form has skipping properties, like in Textbox_Q1 if the answer is A then skip Textbox_Q2 and go to Textbox_Q3, by that process Textbox_Q2 will be unable and the blinking vertical line (just like when your typing in Ms Word) will move to Textbox_Q3. The Question is how can this happen UPON TYPING the VALUE (what event handler), without pressing enter or clicking the next Textbox. By the way, all the answers per Textbox, or even the value in each dropdownlist or Radiobutton are just two numeric digit. (00 - 99).
Validation:
In the Survey form, there should be a validation on each controls even though there's a possibility that some other controls will be skipped. the validation is just two, 1st is it should not be BLANK and ...