What version of the Windows Operating System are you running?
Either way, this article will point you in the right direction to all the information you need. The memory section will detail all the books online articles you need to reference.
An appropriate example configuration, if you are using the /3GB switch and a Windows Server 2003 Enterprise Edition might be:
Factors other than solely the amount of RAM your server has available influence what would be an appropriate configuration. For example, if you are using a lot of CLR components or SSIS packages, you may wish to ensure that more memory is available from the memToLeave area of the buffer pool. To ensure this you would need to use the -g startup parameter for the SQL Server Service and would also need to reduce the MAX memory setting of SQL Server accordingly.
I hope this info. helps you along the right path to choosing an appropriate configuration for your platform but do please feel free to pose further questions.