Regarding F4 help(VERY URGENT)

Hi,

i have desigend my own selection screen in tht i am having one table control in tht i have say two fields

one projectid and objectid first user will press F4 help in the projectid he will selcet his own projectid and then when he presses F4 in the objectid only corresponding object of wht he selected before for the project id should be displayed see for my requirement F4 will not trigger PAI but based on wht projected id he entered he should get objected id so can any help me on this

plzz i will reward for sure

thanks and advance

Sunil kumar Mutyala