i was wondering how can i get the particals to hrmmm… vibrate back and forth on x axis not alot just a little bit ?
A force field? What effect do you want?
simple back and forth motion can be done with the Time IPO.
an a sort of related note, for really amusing particle motion, create an gracity object with a large range. Inside of it create a significantly stronger negative gravity (repulsor) object with a small range. duplicate. Add the emitter(s), and enjoy the show 
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