A family of Microsoft relational database management systems designed for ease of use.
The only way to do this is through VBA since you have to loop through the days to check each one as to whether its a weekend, holiday or weekday.
You put the code in a global module. Then call the function like you would any built in function.
Sorry I missed that you want to add dates. On the same site there is a group of Workday math functions which includes an AddWorkDays function: http://access.mvps.org/access/datetime/date0012.htm