configure ut 300r2


hi,actually i got broadband connection from bsnl. they provide a "UT STARCON ADSL MODEM" but we have 150 pcs in office and i want to connect all pcs to internet.i also have router and switch (D-Link), and firewall (watchguard)but this modem is only for one pc. i was trying to connect all pcs. i connected lan cable in to switch. and defined gateway "" in network property. but i was unable to access. pls tell me how to do solve dis problem. and how to dial connection to internet when modem is connected to switch. b'coz it connect via dialupwhen i open my router property and define gateway "" but i got message "bad gateway"..thanx in adv