Windows Updates - Visit this website, at least once a week to download the latest security updates and patches for Windows.
Antivirus and Antispyware
Ad-Aware - A great free antispyware utility. Use in conjunction with Spybot
Spybot - Another very useful utility to get rid of spyware on your machine.
Panda ActiveScan - Free online antivirus scan.
Trendmicro Housecall - Another good free online antivirus scan
Why Don't High Speed Modems Work at Their "Rated" Speed? Very good reading, tons of information
TechSpot - Tweaking your modem
UpsetChaps Gaming Connection Guide
Awolfpup's Guide to Speed Issues