Automating Tax Forms for Donations

[ZHarvey]

I am a software developer building a website that will allow people to make donations to one of several charities. When a donation is made, I would like to automatically send to my users 2 things:

1. A receipt of their donation/financial transaction; and
2. Some sort of tax form that they can use to claim as a deduction or something similar

Although this question forced me to pick State or Federal, if there are different tax forms I need to send for different states I am interested in knowing what those are too.

So basically here are my questions:

1) What are the different tax forms I would need to send?
2) What are my options if, say, they make a donation through their credit card and then dispute the claim (and the credit card vendor reverses the charge)? Now they have a tax form (that we automatically emailed them) that says they made a donation when in fact they did not!

Thanks in advance.

[Mr. Knowitall]

You can issue a receipt that they gave money to you, but unless you're a tax-exempt charitable organization in your own right, you can't give them a receipt that would allow them to take a deduction on their taxes. If you want to turn yourself into some sort of online United Way, a tax-exempt charity that accepts donations and passes them along to other charities, you will need to become a 501(C)(3) organization.