How to stipulate default applications in GNOME

[AG <computing.account@googlemail.com>]

Hey list

In GNOME, if the options selected under "preferred applications" for 
browsers doesn't get applied, how can I set an application to be the 
default?

Case in point: I use Kmail & Icedove, and want Iceape as my default 
browser for clicking links, etc.  Icedove remembers this and complies, 
but KMail keeps opening Konqueror.  I seem to recall that there was a 
way I could set up a default, but don't remember the specifics.

Also, whilst on this topic, is there a centralised location in which all 
these kinds of commands are listed?  I've looked through the wiki and 
cannot lay eyes on anything, but I had in mind the commands to set 
sun-java as the default (I do know how to do that), set default 
applications, etc.  The wiki has the instruction on setting up 
flashplayer-plugin but I was hoping to find maybe a list of these tips 
and tricks that the seasoned veterans would know.

Any ideas?

Thanks - as always.

AG