If you have the SQL Server 2008 Installation media, you can install just the Client/Workstation Components. You don't have to install the database engine to install the workstation tools, but if you plan to do Integration Services development, you do need to install the Integration Services Engine on the workstation for BIDS to be able to be used for development. Keep in mind that Visual Studio 2010 does not have BI development support currently, so you have to install BIDS from the SQL Installation media and use the Visual Studio 2008 BI Development Studio that installs under the SQL Server 2008 folder in Program Files if you need to do any SSIS, SSRS, or SSAS development from the workstation.
As mentioned in the comments you can download Management Studio Express free from Microsoft, but if you already have the installation media for SQL Server Standard/Enterprise/Developer edition, you'd be better off using what you have.
Download SSMS 2008 Express