These are the setting for the modem used with StarHub Adsl for office use.

PPPoA

VPI/VCI = 0/33

username: xxxxxx@webspeed.com.sg

password: xxxxxx

The most important thing is that it is PPPoA and not PPPoE.

Now if we what to use the modem with PPPoA and still get the public ip on our router, here is a possible solution from the following website.

http://forums.whirlpool.net.au/archive/1467556

LI commands: (Telnet into modem e.g. with puttY, default password is "Administrator" and password is blank. Case sensitive!)
=>:system reset
=>:ppp relay flush
=>:eth flush
=>:atm flush
=>:ppp flush
=>:atm phonebook flush
=>:saveall
=>:atm phonebook add name=BrPPPoA_ph addr=0.33
=>:service system modify name=PPTP state=enabled
=>:saveall

and then I followed the Pdf Config guide at
[7.1.2 Configuration Procedure for Routed PPPoA with DHCP spoofing]

The pdf is attached here.