Help On Sums - Dates This Time + Rewriting Of Data

The Database is coming along nicely now, but in need of guidice with this one:

On the main table of the contacts I have what you could call a date of 01/01/06 and a combo box next or below that that I select what risk levels to asign the user.

Each user would have a no of year review based on the risk level:
High = 1 Year
Med = 2 Years
Low = 3 Years.

There is another date box that is blank at the moment, what I am looking for query wise or another way is on change/update the risk level is to add the start start in this case 01/01/06 (if user is Med Risk - then add 2 years) and adding risk level giving me a new date of 01/01/08 in the blank date box (this option will make the main table update.

Can anyone point me in the right direction for this one?

Thanks

Mike