For those having difficulty using wifi tether after rooting, I had a similar problem. I loaded the Pre-9 version of the software and got my Win7 laptop connected just fine; and also a Vista laptop. But, I could not get a 2nd Vista laptop to work. It would connect, but no internet.
Then, light bulb, I noticed that my wife had accidentally or intentionally turned on the windows firewall. This had not been a problem in the past using an ad hoc network on WM phones, but now it won't work.
After turning off the Windows firewall, everything is great; good speed, multiple connected computers. I don't know how many connections are possible, but I've had up to three.
Hope this helps.
St. Louis, MO