I am curious of this answer myself. Because from what I have read this is an impossible feat. Even if rooted.
It's entirely possible. You have to remove the relevant .apk and/or .odex files directly from the /system/app directory. You can do this using the command line from an ADB shell or (much easier) download Root Explorer from the market and delete them as you would in any other file explorer--there's a little button on the top right that mounts the directory with R/W permissions so that you can delete things.
Once you've removed the packages, reboot so that the phone will restart without loading them. Voila!
Make sure you know what you're deleting, by the way.