WM the OP is probably talking about a 3g dongle. If the modeswitch is an old version, it would not be recognised no matter what (live CD or not).
The thing is that in order to get the latest modeswich you need to download 2 packages (they are in the repos) plus two modeswitch files with the new data.
This can only be done if you have internet connection. When you buy a 3g dongle it comes with a CD with drivers (or the drivers are installed internally) but it's only good for windows or MAC.
For linux, either you are lucky and the ID of the dongle is recognised automatically by the "old" version of modeswitch, or you need to download and install the latest one.
The other method I have found which is very easy and helpful is to install and run "sakis3g" program.
I can give the link to download it so you can do that from another PC that actually has internet connection and then transfer it to the PC that does not have internet connection via a USB stick.
You just download it, right click it > properties > allow executing as a program and then double click it to run it.
You follow a set of easy questions and hopefully at the end you get connected. It has the option to even create a desktop shortcut which you can use to connect/disconnect. I think its much easier than modeswitch. Maybe I should prepare a guide about it at some point.
It is completely separate though from network manager (unlike modeswitch). This is no big deal ofcourse.
The link is here:
http://ubuntuone.com/483w3IX72DN3lOlGFcrxQKI have uploaded it onto my ubuntu one account.