Webpages failing to load

Hi everyone, this is my first post, but knowing Windows it won't be my last!

I have recently setup a MS windows 2003 Small business network, with ADSL shared access to the Web. The network is running fine, email is collected without problem, directories share happily, things are all quiet on the LAN front. Unfortunatly not on the Web front.

I have a client who uses the web 50% of the day, he goes to a range of sites including ebay. Some days the sites load up without a hitch, sometimes the sites need two or three attempts with the refresh button before they load, sometimes (and this is the real problem) they fail to load after each new page, so when he is conducting business on ebay for example, it takes an age to perform simple tasks because he is constantly refreshing pages and going back.

Can anyone point me in the right direction, I am using a Belkin Wireless ADSL modem and BT Internet.

Your help in this matter would be greatly appreciated as it is causing him and me to tear whats left of our hair out!

Barry