I agree with Christine, take the image in colour, preferably in RAW format, and process into B&W on the PC afterwards.
If you take the picture in B&W using the camera's built-in B&W mode, it will decide how to do the processing, and then you're stuck with what the software engineers at Canon thought was best. If you take in colour, you can decide how to process the mono effect.
If you take the pictures in RAW format, you have complete control. You can convert the raw files using the bundled software that came with the camera to be just like the jpegs you (may) normally take. You can use the same software to process them on the PC as though you'd shot in-camera B&W. The difference is, by shooting raw, you have the "master" file that you can process any way you like. If you have a jpeg, you're stuck with that as a "master".
You can always go from raw to jpeg (colour or mono), you can't go mono to colour and you can't go jpeg to raw. If you shoot raw+jpeg, in-camera, you have the best of both worlds.
There's plenty of mono processing tutorials and photoshop add-ons, my own favourite for quick and dirty mono processing are the conversion actions and toning actions you'll find here:
http://www.thelightsrightstudio.com/photoshop-tools.htm
If you're a bit daunted by using actions, a primer is here:
http://www.thelightsrightstudio.com/...tionBasics.pdf
Hope this helps.
Duncan