Network Bandwidth monitoring

I plan to incorporate my MRTG system into Xymon. I would like to know if I can have a "Red" alert appear when my bandwidth utilization of a particular interface exceeds a certain amount over the 5min interval?

Is this possible?

If so, can you point me in the right direction so I can research how to set it up?

I have a DSL circuit I need to alert when it reaches the 500Kb upload rate.

Thanks, Mike