Conditional Formatting – Heavy boarder to the bottom every fourth row

I am designing a multi-page sign-in sheet that I would like to have the bottom line of every fourth row formated to be a heavy line to stand out from the rest to facilitate “time-in”/”-out” entries being written on the form.

The sheet has pre-printed names, one for each row. These change on a daily basis and are updated via “cut & paste” from another excel sheet.

In addition, the form has 12 “in”/”out” columns per row and I would like to apply 10% shading each of the 6 “out” columns.

I would like to be able to cut and paste new names onto the sheet or add / delete rows without having to reformat the cells all the time. I believe that this can be done by using conditional formatting but do not know what formula to use.

I am using Excel 2003.

Can anyone help?