I have the same setup (D620, Vista, built-in BT adaptor). I have been trying to get the Wiimote to talk to the laptop using the standard Dell-provided BT driver. I have not tried BlueSoliel yet (since I don't understand what it is for I didn't want to introduce another complication).
I can sometimes get the Wiimote to show up as a connected bluetooth device by adding it from the bluetooth control panel applet. It is not reliable, however. Often if the wiimote is turned off and back on it doesn't seem to connect.
Once, I was successful in connecting to the Wiimote using a test program that I found on the net. That program was able to display the status of button presses, and the distance calculations from the IR sensor (sorry, I can't remember the name of that program and I don't have the D620 here.) So there is some hope.
However I have not been successful with Johnny Lee's DesktopVR app, nor with the test program that comes with WiimoteLib. Both give an error indicating that they can't find a wiimote connected. I modified his app to use the latest version of WiimoteLib (1.2.1) but still no luck.