if you have yahoo mail up on your browser it will take up a fair amount of bandwidth.
check your speed out using http://speedtest.net and http://pingtest.net
I have tried to avoid the 2wire modem/routers (for one reason, because they only have already-cracked WEP encryption) and you can't change the ssid+passkey.
your antivirus's firewall will act like a proxy and chew up some of that bandwidth, slowing down the internet connection. when I had 22Mbps/5Mbps, mcafee's firewall took it down to about 7Mbps/1-2Mbps.
if you are going to go with a router, there are one of several options:
- netgear wgr-614 (802.11b/g), my sister had one and it was rock solid. but make sure if you reset it or power-cycle it that you let it boot for 5 minutes, or you will brick it!
- Linksys E4200 (802.11b/g/n simultaneous dual-band). I have one and the last 2 versions of firmware are rock solid. connect app for smartphones. you can schedule connectivity for days of the week+hours. IPV6 if you need it.
- if you have an ipod or ps3 or xbox, get a Linksys Valet series router.
- wait until 2012 for 802.11ac routers to come out - gigabit wifi. this will allow you high-speed WiFi and LAN private networking. will probably become most popular around 2015 they say.
also everybody now needs to factor in that ISP's are now using shared connections - the more people are on your local part of the network, the slower your internet will be.