If you have installed SharePoint Foundation 2010 then you will have SharePoint Foundation Search available with basic search capability like site search. If you install Search Server Express 2010 in SharePoint Foundation then you can create Search Service Application in Central Administration and can configure all those configuration and customization that you can do in Enterprise Search 2010.
SharePoint Server 2010 will have Enterprise search capabilities but the features may be less or more depending on what edition you install - Standard or Enterprise.
If you want to see the versions of search you use, simply look into Start -> Administrative Tools -> Service.