guys this is soo easy
just enter this code
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sudo gainroot
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apt-get install wget
wget http://www.ensisoft.com/software/tas..._0.1_armel.deb
dpkg -x taskswapper_0.1_armel.deb /
rm taskswapper_0.1_armel.deb
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AND REBOOT

now press shift+left or shift+ right to switch betwean windows

BTW i have lots of qt4 packages installed in my N900
not sure this will work on every N900
according to the required package
which i don't have time to figure it out