Creating a form where you can tick a selection

Hi,

This is quite urgent if anyone can help!

I have to customise a form in word where the aim is to be able to select a variety of options using check boxes - and then have a sum at the end, of a column next to these check boxes holding info about the length of time it takes to perform these options.

Inserting check boxes is simple enough - but how do I start to add up a column and then convert the numbers into time - and how do I begin to get a macro in there so that what is added up at the end is only what has been selected by the check boxes down the side?

Please please please help!!

Thanks
Sarah