How do I protect a certain area in an excel worksheet without interferring
with the rest of the document?

Highlight all the cells in the worksheet, either by CTRL-A or by
clicking the box intersection of row and column identifiers. Then
Format | Cells | Protection tab and uncheck the Locked box. Then select
the area which you want to protect and Format | Cells | Protection tab
and check the Locked box. Then Tools | Protection | Protect sheet. You
can specify a password (twice) if you want to increase the protection.

Hope this helps.

Pete