Is there any way to improve the downloading speed?

Your Question is incomplete... U ven't told us which connection u r using... in case of Dailup which modem u r using? ... in case of router which router u r using? Do u have any Firewall system installed? Do u use any antivirus and spyware? Do u update your windows regulary? if yes let us know.. Then We we will able to assist u in that case only

I am using wireless networks. operating system is windows vista home basic. norton antiwirus and adaware is installed in the system.

Logged with administrative.
Run command prompt, at Command Prompt, type the following command.
netsh interface tcp set global autotuninglevel= disabled
This command will disable the TCP autotuning feature. Now restart your computer to get effect.

Note: Check the security regarding this tip before implementing

thanks for that rahul