Did you not get any discs with your camera - the software is on there, upload it to your PC, then jump on to Canon Europe's web site and you can install the latest version from there - they are all free, but are an upgrade, not initial install. However, I believe there is somewhere you can upload the original software from Canon's site, if you don't have the disc, you need the serial number of the camera...
I'm sure someone will be along shortly and point you there, if not, let me know and I'll see if I can get you a copy of the original software...