I was trying with MacPorts - it gave me the following error..
:error:configure db46 requires the Java for Mac OS X development headers.
:error:configure Download the Java Developer Package from:
:error:configure Target org.macports.configure returned: missing Java headers
:debug:configure Backtrace: missing Java headers while executing
By going through some of the MacPorts tickets found out that we need to have Java for Mac OS X 10.6 Update 3 Developer Package installed first - which you can get from here.
Once that is done, only following is needed..
$ sudo port install scapy