You need to create a linked server using sp_addlinkedserver procedure

EXEC sp_addlinkedserver

@server='TestServer',

@srvproduct='',

@provider='SQLNCLI',

@datasrc='YourServer\InstanceName'

Then, create linker server login

EXEC sp_addlinkedsrvlogin 'TestServer', 'false', 'sa', 'sa', 'password'

Thats it.

Now query the server,

select * from TestServer.master.dbo.sysobjects