If I create a listing as you suggested, under the select a suitable category tab in the advanced tool (which is where I am assuming you are), it doesn't appear to give the option of a second category. However, under the suggested category tab, it does give the option of 2 categories. That said, the category can only go as far as computers>enterprise networking servers>servers and I'm not sure if the other category you want is in there.

I just inserted the word computer in the title.