Well the next time you want to upgrade the memory on any HP model a look at the product information or following the steps outlined at their support site will help out considerably. http://h20000.www2.hp.com/bizsupport...odTypeId=12454
The link there is for the a6170 models in general since no a6170n but a few a6170 links were seen there. As far as getting advice in retail stores where they hire people simply to sell you often have to look past the advices on some things they offer.
Their jobs putting it simply are to "sell" and you got caught on that one!
Knowing what you are looking before going into any store like that will help you avoid making any big ones. Remember you can easily end up spending a small fortune on this stuff very quickly if you don't keep yourself informed by first looking into things like system specs and what will work.