New columns or new table alltogether?

In a project I work in we have an SQL Server database full of data (meaning thousands of rows). The need for new columns however has appeared. So far we are inserting new columns one by one via our C++ framework (using insertcolumn e.t.c). Would it be more efficient to create a temp table to store the data, create a new table with all the extra rows needed and then transfer all the data to the new table?
We are using SQL server 2000 over windows 2000.

Thank you