I am not sure why people are so obsessed with vardiff. Changing the difficulty of submitted shares does nothing to find blocks faster or slower. I was fine at middlecoin with diffs of 1024. The pool doesn't get paid by shares, it gets paid by blocks. I just like the website here better.
Because we have one crappy card, and 516 is too hard for shares.
Because you have a crappy card the whole pool must change for you? are you serious? are you a spoiled child?

ohh and its 256/51
2/1024
No, dude, you don't get it! If you are mining for longer than a few hours it doesn't matter at all. Crappy card or not, your hashes submitted will always have the same chance to get a share at any time. With a higher difficulty the only thing that changes is the variance, which averages out over time.