[ale] Any suggestions re: bandwidth partitioning?

[reggie at busicast.com (Reggie Euser)]

I'm looking at installing 3 bonded T1's to be shared between 2 companies.
I'd like to create a fixed partition so one company can use up to 1Mbps but
no more and the rest of the bandwidth would be dedicated to the second
company. The ISP doesn't offer that configuration or a configuration
capability but says we can do what we like.

Any suggestions re:  solutions?

Is there a linux solution that would do this via some sort of intermediate
gateway?

I've looked at a number of appliances, but really don't want to spend $2500+
on a box if I can help it...

Thanks for any help!