Can any body tell me the software I can use to limit the bandwidth of system, the problem is that I 20 system I phone call and using.

Since no one else had tried to answer this question -- I decided to try

Limit Reservable Bandwidth in Windows XP: DIY Hack « THE11thROCK Technologies

limit the bandwidth of system - Google Search

Hope this helps -- Some times you get lucky

Biggsie,
You may be on the right track. The Local Group Policy changes mentioned in one of the articles will help free up some of the reserved bandwidth that Windows XP keeps aside.

This is a tough one. Bandwidth throttling is readily available for web servers to control web site access. Windows IIS has bandwidth throttling capabilities. Probably not what you want.:(

IP Prioritization and Packet Queueing using QOS rules is typically performed within a fully managed Layer 3 switch. At the cost of many hundreds of dollars, it is unlikely that you find these in the home network. Even in our sizeable company network with about 1500 nodes, we only have about six of them.