Validate a field (input box) and how to show a window.

Validate a field (input box) and how to show a window.

hi friends, i think this question is easy i explain my process:

1) i have 3 fields, and 2 buttons (SAVE and RESET)
   1) Capture NAME
   2) Capture TITLE
   3) Capture AGE.
Initially the 3 field have a empty value.

I start capture the NAME (if here the user click on SAVE button) i need show a message, saying: "Need Capture AGE" and focus to capture AGE field.

i know how do it but after subbmiting the data (with php, check and do nothing)... but i think exist other wa.

Note i searched on the forum before ask.

2) how do this capture in a float window(and too the validation).

any sample?

thanks