Your psu is a 300 watt. You MIGHT be able to get by with it, but I wouldn't try it. I used a trusted psu calculator
and got ~260W, with the system load setting at 95%. There's still some breathing room there as the regular setting is 90%, but still....I wouldn't try it.
edit: whoa, problem. Your case is a BTX model, which is a stupid design that HP, Dell, and a couple of others are using. Everything is either backwards, in the wrong spot, or a different size. A standard ATX one won't fit. Gimme a second, I'll try and find one that will fit.