I just installed Tether and it works... Kinda. I have it connected but I have no internet through it. The Blackberry can still access the internet, but no connection is available on the laptop.
I have a Blackberry Bold 9700 and work with Internet Explorer 8 on Windows XP Pro.
Blackberry firmware is: v5.0.0.423



What does the Tether log say on your BlackBerry?
With Tether running and visible click the BlackBerry key and select "View Log".
What does Tether say on your PC?