Why can't I use my phone as a modem?

I've got a 3 phone on contract, and I've download the nokia pc suit for it,
and on my dads pc it lets me use my phone as a moderm but on my pc or laptop doesnt work at all..it just keeps coming up no modems found :/
what could the problem bee

Firstly, does the phone need any software to be installed on the computer for it to work, and does your PC or Laptop have that software installed? And secondly, how does the phone connect to the computer - USB Cable, Bluetooth, some other way? and if it's Bluetooth, does your PC or Laptop have Bluetooth as well?

USB CABLE, I've dwnload the disk what came with the phone onto the pc its called 'pc suit'
thats all I did on my dads pc and it worked:s

Odd - the only thing I can think of is that perhaps their is some sort of annoying thing that only lets the phone be used as a modem with 1 computer, in which case it would be your Dad's. I hope that's not the case though!