Hopefully this will address any steam-related issues, but feel free to post any problems here.
Also useful: Hanfling's custom DX launchers http://coding.hanfling.de/launch/
These counter many speedstepping and multiple-core processor issues, plus are effectively exactly what you need for the "steam-version Deusex.exe"-replacing guide outlined by Master_kale, above.
And further usefulness: link to chris dohnal's renderers page: http://www.cwdohnal.com/utglr/
Both the openGL and D3D renderers are great.
