Check out
www.grc.com to see how good your firewall actually is. Use the 'Shields Up!' program, and that 'Port Scan' program. They are run via the web - you needn't download anything.
Broadband IPs are well know, and sequential - the hackers know that everyone between IP #xxx and IP #yyy are broadband (i.e. that they are ALWAYS online), which makes them the easier targets, therefore, they attack all of them. It is not a direct attack on your computer - you are being attacked with everyone else using your service. Why, isn't that nice!
anyway,
www.grc.com should let you know how you stand. If you care to, read those pages in FULL, and you can change your networking windows piece of crap into full stealth mode, and hackers won't even know you exist.