I'm using 2002 here but I'm sure 2003 is the same. You can stop users
from changing your cell  border by:

1. unlock the cells  you want them to be able to change  the numbers in
(Format, Protection, untick the Locked box)

2. protect the sheet (Tools, Protection, Protect Worksheet) in the box
that pops up tick boxes to allow users to select locked cells and
unlocked cells but don't tick the boxes to allow them to format cells -
up to you whether you use a password to protect the sheet - depends how
determined your users are to change your formatting!

3. press OK.

You should now be able to change the numbers in the cells - but not the
formatting.