I just noticed this...I have .bmp listed in my allowed attachment extension list, yet when you insert the URL of the .bmp picture into the image tags you just see the line of code, not the picture? Any ideas??

You should not upload bmp images to display in the internet. Period.

If you still want though(which you shouldn't), you should add the bmp ending into the regular expression that does the substitution,
in ubbt.inc.php , in the part
// Convert image markup