Help 78,
I used to have a nokia n97 that runs on symbian and I used to connect the phone to my pc using the nokia usb cable. After the pc having installed the mobile phone drivers you can check and see if you phone appears in the "Device and Printer" folder of windows. There should be two icons of the nokia, one for the storage device and the other for the nokia 6790.
I have set an example for you on the pictures attached, (note that this can be made with a pc that has a bluetooth device connected).

Step on how i did it,
1. go to Devices and Printers folder > right click on the phone icon > Dial - up Networking > create a dial-up connection
2. choose the first bluetooth modem selection (if it doesn't work try the others just in case)
3. In the Dial-up phone number write *99# (I don't remember where I got this number from but it has worked for me on the N97). Leave Both Username and Password in blank. You can also change the Connection Name if you like.
4. press connect button

Note,
I am using windows 7 and i think that vista also has the same feature of this kind