need drop down trick

hello frd


can you help me to sort out this small matter



this is my simple question

Area Chetan Amit raj mehra
New Delhi 1 1 1 1
Old Delhi 1 1 1
Uttam Nagar 1 1
Tilak Nagar 1
Janak puri 1 1 1 1

i want simple drop down
for example
1. if i select chetan then only show in drop down new delhi, old delhi, and janak puri (not showing uttam nagar and tilak nagar)
2. if i select amit then only show in drop down new delhi old delhi, uttam nagar, tilak nagar and janak puri
and future if chetan want to see the uttam nagar (if i selected 1 in chetan at uttam nagar ) than show in drop down list


can anybody tell me the trick or something tips in drop down