like ta-t3 said, you can use load applets to start the process. I have osso-statusbar-cpu installed, and use two custom commands to take screenshots using the below code to call osso-screenshot-tool. the code takes a parameter of seconds (0 or 3 or whatever you want).

the custom commands that i have are:

Desc: Take screenshot now
Command: sh /home/user/sShot.sh 0

Desc: Take screenshot - 3 secs
Command: sh /home/user/sShot/sh 3

this assumes that you have the osso-screenshot-tool installed, and that the code below is in a file called sShot.sh and is located in /home/user/ and is set to executeable ("chmod 700 /home/user/sShot.sh" without the quotes, from command line using xterm). i also use flite to synth the completion. you can comment it out, or remove the line if you dont want to use it.
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#!/bin/bash
sleep $1

stamp=`date +%Y%m%d-%H%M`
i=1
path=/home/user/MyDocs/.images
if mount | grep -q mmc
then
path=/media/mmc1
fi

while [ -f $path/shot-$stamp-`printf %02d $i`.png ]
do
i=$((i+1))
done
osso-screenshot-tool $path/shot-$stamp-`printf %02d $i`.png
flite "Screenshot complete"
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