Here's a tip: why not simply delete the IE icons and make Firefox and/or Chrome your default browser? That way, you can continue to use the "IE-Tab" Firefox extension (as needed), you won't have to use IE to run any Windows Updates since you're on Vista, and you won't adversely impact any third party applications that might use IE "under the covers" to handle web content.
Deleting the icon gives you the perception that IE is "gone" from an "out of sight, out of mind" perspective.
The best thing is, deleting the IE icons is very easy to do!
Peace...