I run copilot 2003 due to the screen size issues, but the maps are farily dated.
I use the I-Bus for volume control and app switching. The only software I have for it is some stuff I custom wrote into my in-progress application. You will not be able to do much with the I-Bus since you kept the radio. If you don't have the BMW phone (seriously, who does) you can trap events from the two phone buttons on the steering wheel. You may also be able to send commands from the pc to the radio to tell it to switch modes, etc. There might be a way to output some text to the radio screen also. Look to the HackTheIbus group on yahoo groups for more.
As a side note, I get more emails and PM's from people about the I-Bus than anything else. I think I have said this before, but please do not contact me (sometimes repeatedly) about I-Bus stuff. I do not have any software that works under windows to do anything with the I-Bus. I abandoned my efforts under windows a long time ago. I also, do not know very much about the I-Bus aside from using it to 'listen' for events. In all likelyhood, using the I-Bus will mean that you are going to be writing your own software to communicate with it. /End PSA