This service pack is now available to Subscription Service customers. To download, click here. Or log into the SolidWorks Customer Portal at https://customerportal.solidworks.com and click Download Software and Updates to access the update. 

Note: If you installed the hotfix for SolidWorks 2009 SP5.0, you should uninstall that hotfix before installing SolidWorks 2009 SP5.1.

For a listing of SPR’s fixed in this Service Pack, click here..

Source: www.SolidWorks.com