jquery.jparallax.js vs 0.9.1 with jquery.fancybox-1.3.4.pack.js using jquery 1.4

jquery.jparallax.js vs 0.9.1 with jquery.fancybox-1.3.4.pack.js using jquery 1.4

I seem to run into this problem quite often.  When combining some plug in's (in this particular case  jquery.jparallax.js vs 0.9.1 with jquery.fancybox-1.3.4.pack.js using jquery 1.4) the conflict things seems to rare its ugly head. 

I'm not sure I understand why some plug in's conflict with others or what I need to concider for I get any more bright ideas about using multiple jquery plug in's to work together. 

What is the best method for trouble shooting jquery conflicts and/or getting multiple plug in's to work simultaneously with different versions of jquery itself. 

Thanks a million!