Generally remember to install Topfield software before connecting USB cable.
This is written for XP If things go wrong then disconnect the Toppy & completely uninstall Topfield Applications & Boot up in safe mode and then use Device Manager to properly remove any/all Topfield devices.
Check you have no files named 'topfield*.*' or 'tfbulk*.*' anywhere on your system - if so delete or rename them.
Download and install just Altair from Topfield Utilities.
Put these files in a known place - TfBulk.inf & TfBulk.sys.
Reboot the PC in Safe Mode and log in as Administrator.
Start Device Manager and page to the bottom so you can see USB devices.
Turn on your Toppy. Plug into the USB and Windows should detect it. Folow the wizard and install the drivers from wherever you put TfBulk.inf & TfBulk.sys. Hopefully these will now install successfully (though it will tell you they won't work until you reboot).
You should now see the Toppy as a USB device in Device Manager.
Leave the Toppy plugged in and reboot.
Look in Device Manager - the Toppy should be there?
(It is not generaly expected to be needed to reboot the PC but as this worked for a couple of people who were having problems I have written it in here)
Also a guy in the forum reported success after problems post SP3 here