adding field in pa30 screen urgent

hi all,

i am new to user exits.

and my requirement is to add a field in screen for PA30 tcode screen.

so how i can go for this .

if anyone has added fields in any SAP standard screen

then plz give me the doc regd that with screen shots if u have otherwise give me the steps.

my mail id is- sanjeev.singh@prospectasoftware.com

plz i am looking urgently for it.

i will award all ur efforts.

thanks

sanjeev