Here are a few options.

Devil's Pie

Here's an old tutorial.

wmctrl

You can make a script to move to the desired workspace and then launch your app (source):

#!/bin/bash

wmctrl -s 1

firefox --new-tab $@ &

Or you could launch your app and then move it. I think something like this would work:

#!/bin/bash

thunderbird &

wmctrl -r :ACTIVE: -t 1

# if thunderbird takes a while to launch, you may need to find the window yourself:

#wmctrl -r `wmctrl -l | grep [t]hunderbird | cut -f1` -t 1

Compiz Place plugin

You can enable and configure this if you install compizconfig-settings-manager .

Allows you to set fixed positions for windows with specific titles.

FYI, previously I used wmctrl in Gnome. Some of its features don't work for me in 11.04 w/ Unity, but should be good in 9.04. Not sure about KDE though.