Vista Internet Connection Tester: Test to see if you need to disable the Vista auto-tuning TCP window scaler.

Handy online site to test your home connectivity capabilities.
You will want to use Internet Explorer on this site for proper behavior.

The "official" description:
The Internet Connectivity Evaluation Tool checks your Internet router to see if it supports certain technologies. You can use this tool on a PC running either the Windows Vista or Windows XP operating system. If you're planning to run Windows Vista, this tool can verify whether your existing Internet router supports advanced features, such as improved download speeds and face-to-face collaboration using Windows Meeting Space.

Test your internet connection here.