Hi I am also on rogers. I just bought a galaxay s through bell.
Switching it to rogers was a piece of cake with the Galaxy S
Here are the steps I took.
1) Go to the market and download android unlock tool and run it.
It gave me the unlock code for the phone.
2) Power the phone down, and replace the bell sim card with my rogers one.
3) When you power it back up it will not recognize your sim card and a prompt will come up to enter in your unlock code. Enter that in and your phone is unlocked.
4 Enter Rogers apn settings and you are all set (you can find these easily by doing a google search for rogers apn setting)
That was it. Less than 5 minutes and no technical ability needed.