Hi,
In a nutshell yes, its very much possible.
Do you already have a FWSM? If not, its really too much horsepower for FWSM deployment in a 3 VLAN deploment.
You may achieve the results with simple Acces-lists also.
FWSM is more for virtualization, where in it can turn each and every port in the 6500 Switch into a FW port.
http://www.cisco.com/en/US/prod/collateral/modules/ps2706/ps4452/product_data_sheet0900aecd803e69c3.html
Hope that helps,
Kind Regards,
Wilson Samuel