If you purchased a computer that came with a BD drive, then you should have some sort of software to play BD movies.
To the OP: HP Blu-Ray issues
OEMs would NOT sell you a Blu-Ray drive without the ability to play BD movies. It's one thing if you custom-build something... but if you have a computer from a major OEM (Dell, HP, etc)... then the software will be included in the package. If it isn't, then contact your OEM and tell them.