I'm currently running KDE 3.5.7.

I use Evolution for my work e-mail and Thunderbird for my personal e-mail. I like to keep these spheres entirely separate. The problem is that the title bar for both e-mail clients starts with "Inbox ..." If I have several apps open simultaneously and want to open Evolution or Thunderbird by clicking on the task bar, it takes me a minute to figure out which "Inbox" I need, especially when there are so many apps open that part of the title bar is covered up.

Is there a way to change the content of an application's title bar?

Thanks.

A nice guy over on the Arch Linux forum directed me to this add-on for Thunderbird which let you change the title bar:

http://forum.addonsmirror.net/index.php?showtopic=233

If you use an older version of Thunderbird, you might need this instead:

https://addons.mozilla.org/en-US/thunderbird/addon/757

I've tested the newer version of the add-on with Thunderbird 2.0.0.6, and it works great.

Have you taken a look at dcop ?

Well, I just did (at least here http://developer.kde.org/documentation/other/dcop.html)
but, not being a programmer nor the son of one, I didn't see the connection.

That's OK, I completely understand.
I looked at dcop some while ago: It seemed very clever, flexible and useful, but I did (do) not have any particular problems that it might have solved for me, so I just put it aside.
But I think it'll do what you want (and much more). As an example, copy & paste this into a konsole window:
Then check your konsole window's title bar.
See what I mean?
Sorry, I do not have links to tutorials and such, because I do not need it (dcop) and am way too busy with other stuff, but google is your friend!
Happy searching.