get a hold of one of the word docs that causes this problem. possibly it will turn out to be 'complex' document with graphics or such.
then find somebody who can print it successfully and somebody who can't. go to printer, get self test page. take to working pc and compare printer drivers on the two systems. maybe you want pcl5 instead of 6. paw around inside printer properties on working system, check out all the options, make notes. maybe driver doesn't correctly know how much RAM printer has. maybe sending RAW when better sending EMF or vice versa. see? you may prefer to cut to the chase by checking hp website for this problem. my money on RAM settings. upgrade to latest driver version on bad box(es) just because...