Am I screwed for ordering this graphics card for this PC?

erh yes it will last and since you have a Pentium D which is quite a weak CPU, the 5570 is the best video card that you can choose without bottleneck

Are you sure? I don't know what bottleneck is but I'm assuming it's running really close to the PSU limit...
Should I keep the order? I'm going to be playing games and stuff with it

@linh
it's not a D it's Pentium E5300, so it has quite a lot more oomph than an old D model..
(and it says the mobo will support c2d E7xxx series if an upgrade is wanted/needed)

and 5570 maxes out at 38W (well call it 40W), so it should work just fine with that low power psu, especially considering the e5300 isn't a power hog either.
http://www.techpowerup.com/reviews/Powercolor/HD_5570/2...

anything more powerfull than that would preferably need a psu upgrade as well though.

Oh in that case you can probably go up to a HD 5770.

And at OP, a bottleneck is when the GPU is running faster than the CPU and since the CPU can only be so fast, it slows down the GPU. The faster the processor, the less bottleneck there will be when using a graphics card.

Actually it's when the GPU is pushing more data than the CPU can handle, speed of GPU or speed of CPU is only relative when it comes to the speed at which data can be processed and there are other factors to take into account as well such as HDD's and RAM which is why I dislike the way the term "bottleneck" is bandied around so much.

I'd ad a 'would' in there as well
"it's when the GPU would be pushing more data than the CPU can handle,"
 

It reads OK as far as I'm concerned but if you wish to write your own explanation then by all means feel free to do so. And "add" is spelt with two d's.

  darn I always get them mixed up, not being native english speaker.... it's like my 3rd language lol
but yeah, I guess he gets the point about bottlenecks