>In a table having about 26 million records and counting, it contains only a few fields however, what would be the impact of using Char(100) field VS Text or NVarChar field, whatever the field type which would be used? The reason I ask is that the first 26 million records won't have a value in this new field. It is just a caption to enter some text about upcoming images. The table takes 30 GB presently totalling the data + index + reserved. Whichever field type I choose, would there be a space advantage of one over the other or this doesn't matter in SQL Server?

You definitely need to use nvarchar() and not nchar for 100 characters data. If you don't need to store unicode data, use varchar.