Constant values in columns

I have a SQL Server 2000 database used by our ERP system. There are many columns that always have the same value. A table row is really huge, potentially exceeding the maximum row size in SQL Server 2000 (8kB). I'm thinking about replacing these columns with constant calculated columns. This should decrease the size of the table. I expect better performance, because there is less data to read from disk, when the server needs to load the table in memory. Is this a good idea ? Will I obtain the expected performance gain ?