Some things that alarmed me about your post:

gmat580 wrote:I scored a pathetic 420 I don't know how I could of done so poor

I don't think you were prepared for the actual exam. For example, I can probably solve ANY GMAT question given up to 15 minutes to do so. But, that doesn't matter. You get 2 minutes. Also, when you have to do 37 quant questions back to back and 2 essays beforehand you can get fatigued and/or loose focus. There are many other factors, but I still don't think you were prepared to take the test.

gmat580 wrote:I was scoring between 510-530 on Kaplan CAT's and I studied so hard.

Did you just buy the Kaplan book and use that for review? That isn't enough. How else did you prepare?

gmat580 wrote:Does anyone know of a good web-site that would allow me to brush up on basic easy GMAT math? Believe it or not I can handle the more advanced math but I can't get past the easy stuff.

If you can do the hard stuff you SHOULD be able to do the easy stuff. I am taking a guess that you are not able to determine quickly what the problem is:
1)asking you to do
2)pulling what is given and use it to find what isn't
3)quickly determining what you need to do to solve it

This comes from practice, practice, and more practice. Not just working problems, but really analyzing your mistakes and keeping track of them.

gmat580 wrote:Please help I think I might need to retake the test next week to meet the application deadlines.

I advise you to go on the www.mba.com and take a practice test. See what you score on it. If you score much higher than your actual, then you have a good chance of raising your score in a week. If not, then you should think about taking a semester off and studying.

If you can afford a class then you may want to take one. They all seem really good. If you can't afford a class and can only buy books, then I recommend the manhattan GMAT books.

Just remember that this test isn't about how smart you are. It is about how smartly you prepared.

HTH