In SQL 2000 you could write a script using sp_who2 and create a job to run every min and kill connections where ProgramName like 'Microsoft Office%'. That's a pretty hokey way to do things.

In 2008 you can use resource governor to limit CPU and memory by application and limit Microsoft Office to 1% of each so they can't hog resources. This of course doesn't keep them from using MS Access.

Just throwing out a couple ideas.