Sequences W/ Sql Server 2k5

Im doing a quickie Access Project for a Fileroom orginization DB.  Generally, Records are addressed by a 7 character unique ID, with all sorts of rules, assigned by another system.  However we need to track Items that for various reasons do not exist in that system. For this, we enter a code that consists of 2 characters of invalid data, followed by a simple incrementing number.  In Oracle, i would do this with a Sequence.  How do I go about this in Sql Server?basicly, I want to write a trigger that says something like: pseudo code wrote:before insert:   if :new.ItemType is Type3 Then-- File local to our file room      :new.FileID = "IV" + getNextLocalNumber().ToString()   end ifNote that the fileID is not a Key in the normal DB Sense.  It is a neumonicly unique identifier w/ some other properties so that people can easily look things up.