Is your modem plugged in and turned on? (couldn't resist)

I'm an internet helpdesk agent, and although I've not worked with the cable technology before, here are a few simple steps that might get you pointed in the right direction

1) Unplug the power from your modem for a full 30 seconds and then plug it in; at the same time, restart your computer

2) If you're behind a router, unplug it as well...do not plug it back in until a full 30 seconds after your modem has restarted.

3) Depending on your modem, there may be a diagnostic light on it with a name like Cable or Line Sync; If you see *any* flickering on this light whatsoever, contact your ISP's helpdesk and ask them to check your sync rate and troubleshoot if appropriate

4) Actually, it wouldn't hurt to call your ISP and check your sync rate even if your cable/line sync light is solid green

5) Take note of any Windows error messages -- write them down in case you are unable to reproduce them during troubleshooting.

6) Run MSCONFIG (from Start -> Run) and disable any unnecesary services from the Startup tab

7) Run a full virus scan

8) Download, install, and run both Lavasoft Ad-Aware 6 and SpyBot Search & Destroy

Where you have just done a full format of your system, you should have excellent speeds both on the internet and off; there are few chances that anything could be pooched in your operating system. If nothing else, it couldn't hurt to call your ISP and try the slow speeds troubleshooting, and tell them of any issues you have (Don't mention FFXI, just any issues you have with browsing/email, as any internet connectivity issue would affect FFXI)