Suppose the .mdf and .ldf are specifically the AdventureWorks2008R2:
EXEC sp_attach_db @dbname = N'AdventureWorks2008R2',
@filename1 = N'C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\Data\AdventureWorks2008R2_Data.mdf',
@filename2 = N'C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\Data\AdventureWorks2008R2_log.ldf';
Straight out of BOL:
ms-help://MS.SQLCC.v10/MS.SQLSVR.v10.en/s10de_6tsql/html/59bc993e-7913-4091-89cb-d2871cffda95.htm