Firstly I would like to say how sorry I am that you too made the mistake of buying a HP printer. I own a HP Photosmart B110a printer; along with this printer I received a little card which tells me which ink I need to buy on which it says I need 364 or 364XL. Sounds simple enough, or so I thought... It turns out my printer takes a 'specific' type of 364 ink. There are three different types of black 364 ink cartridge; 364, 364XL and 364(*small print* Photo). So HP tell me that my printer uses 364 or 364XL, well thats great! 364XL is better value for money so, naturally, I bought two lots of 364XL ink. Upon running out of black ink I attempt to change the ink cartridge to my new "good value" 364XL cartridge... oh, it doesn't actually work in my printer. So now I go back to Amazon to buy the regular 364 ink, wait 5 days, ink arrives. But is it just my luck? Or maybe I'm just stupid? I have 'mistakenly' ordered the wrong regular 364 ink! It turns out that on the box in small enough lettering that its near impossible to tell from the picture on the Amazon website it says "Photo" - this ink is for a photo printer. Wait a minute, my printer is a HP "PHOTOsmart" printer. I could also mention that the Amazon website does not state which models of printer this ink works with, although I suppose they're probably just as lost as I was.
HP have certainly gone out of their way to make it as confusing as possible to get the right ink for your printer. And if its this confusing for me, who has been working with computers since I was 5 years old... then how is someone less experienced supposed to get it right? Good Luck, I guess. *end rant*