ping your modem with 100 packets. Then ping another site such as yahoo.
If your modem gives you 0 packet loss, which it should, and yahoo gives you any percent of packet loss, it's probably an rf issue not your computer.
If you ping your modem and get packet loss, try changing your ethernet cord.
I have been experiencing packet loss with my cable internet connection. When I ping a web site I get request time out, but not 100%. I had the modem replaced and had the cable company come and check the line. They replaced a fitting to the cable in the basement and was working good but now i have problems again. How do I know if it is problem with my hardware, like my nic card or something else with software. I am running win XP sp2. I did run the diognostic on the network adapter and it was working.