You can set up a bandwidth throttling policy as follows:
Open the Extended Networking menu and select "enable bandwidth control"
You will now see the Bandwidth Control menu appear in the left hand pane
If you're only creating one rule then you can ignore "scheduling"
Go to Restrictions and click Add
Name your new rule and choose the priority level, enter the amount of bandwidth you will allow
Go to the Rules menu and click Add
In the Apply Restriction drop down box choose your new rule
Everthing else should be fine left as default
Choose the Source/Destination tab
Check the "rule is bi-directional" box and enter the IP address of the machine to be controlled.
If you want to control a range of machines you can use the subnet mask, otherwise just enter 255.255.255.255.
Choose the port range you wish to restrict. This can be a problem with filesharing apps because they can use so many different ports. For Bearshare the common ports are 6346-6348.
This should be all that you need to do.