if(cndDateLastModified=="gteq"){stringCompiler+="'CAST(DateLastModified AS datetime)' >= 'CAST(" + DateLastModified + " AS datetime)' ";}////

SELECT * FROM POITable WHERE 'CAST(DateLastModified AS datetime)' >= 'CAST(09/25/2012 AS datetime)'

WHERE DateLastModified >= '2012-09-25' /* ISO date strings are understood and accepted by SQL Server. */
or
WHERE DateLastModified >= GETDATE() /*Everything in the future, time inclusive.*/
or
WHERE DateLastModified >= DATEADD(dd, DATEDIFF(dd, 0, getdate()), 0) /* Everything starting today. */

stringCompiler+="CAST(DateLastModified AS datetime) >= CAST('" + DateLastModified + "' AS datetime) "

CAST(DateLastModified AS datetime) >= CAST('09/25/2012' AS datetime)