Linux operating system show me the low bandwidth

Question

I m using a Redhat linux AS 4 proxy server in my office,in which I configure squid 2.5 for sharing the internet(BSNL dataone leased line).the band width provided by the ISP is 2 mbps,but when I check the bandwidth in http://dataone.in from the proxy server it shows around 400 kbps.

I connect a windows XP based PC to the same port I use for the server in NORTEL 8300 switch.I got the increased bandwidth (around 1.77 mbps). Then I tried the same with another linux based client PC & again I got low bandwith. I use the IE 6 in XP & Mozilla in Linux to check the bandwidth in http://dataone.in

can anybody tell me why linux operating system show me the low bandwidth ?