Motherboard compatibility with this GPU ..?

Alright, have endless hours of searching and question asking, I've finally got my question answered about the GPU I wish to purchase, which is compatible with my Dell DImension E520. But, I've read the motherboard has to be compatible or something? Would somebody be wiling to help me with this? I have a Dell DImension E520, and this is the video card I will be buying : http://www.newegg.com/Product/Product.aspx?Item=N82E16814121442 

Will my motherboard and power supply be big enough to handle it? If my computer only takes about 512MB of it (Because I've read sometimes you can't use it to full potential) but 512MB is good enough for me compared to my 128MB I currently own.

Thanks.

*Note : My Power supply is 305, and I'm not sure of the motherboard.

Thanks