Made a spreadsheet for it (in excel), incase any of you are super lazy / suck at math and can't make it worth :P..
Heres a pic of how it looks:

Download link:
https://rapidshare.com/files/4226910439/Elo Formula_ by Vampire.xlsx
I hope someone can use it ^.^.. It's only the excel file in the rapidshare link, nothing else ^.^..