I can not tell if your HP psu is a standard ATX unit or not. Take some measurements of the back of the unit in your case. If they are standard size (3 1/2" high x 6" wide) then the psu should fit. The Antec unit is not unusually long.
That FSP psu is nice but i'm on a budget. The reason I wanted this antec basiq psu is because i can get it real cheap and I need more wattage. I know all those wires that come with it are gonna boggle my brain! I may need some help with that, lol.