You need to edit the effectors.ltx file under gamedata > configs > misc.
Near the top of the page in the file itself is the following:
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[bobbing_effector]
run_amplitude = 0.0025
walk_amplitude = 0.002
limp_amplitude = 0.010
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Try those values and the bobbing will be barely noticeable. If you want it entirely and absolutely gone (which I believe isn't good, but that's your taste) then leave the walk_amplitude and limp_amplitude to the shown values, but change the run_amplitude to 0.0000, simply. By the way that file is only available if you extract it from the archives with a specific program compatible with those archives. Take note that .ltx files can be edited by NotePad.
I already have that file available since I use and make mods myself for both games so if you want I can just edit the file for you and send it to some hosting web-site like RapidShare, or by e-mail under a .RAR archive if you want with installation instructions of course. If you want me to do it just tell me for which S.T.A.L.K.E.R. is it (SoC or Clear Sky) and it'll only take me a moment.