Do you have SQL Server set up for both SQL Server and Windows on the server? To check this right click on the server, select properties,then tab Security. Under Authentication...

Try it with just this simple TSQL code.

select SUBSTRING(vfield,1,3) + '.' + SUBSTRING(vfield,4,6) from yourtable

For example using string '111':

select SUBSTRING('111',1,3) + '.' + SUBSTRING('111',4,6)

returns: 111.