The Underscore Archives

Hi,
Has anyone done an online giving page with Paypal's system? I need to find a
way for the charity in question to easily see which gifts were from
taxpayers and which weren't.
I'm planning for two buttons (one each for tax/nontax payers) but I'm not
clear on which field to use to obviously mark the payments in their account
view so it's easy for them to add up for the tax return.
I've had a look at their development pages and the hidden <input> fields
look fairly straightforward, but it wasn't clear which one I need to
populate in order for it to be clearly marked in the Paypal account view.
Any suggestions, or are there other ways of going about it, or other
services more suitable for donations? Ideally they'd want the option for
single or regular donations to be set up.
Thanks
- Paddy
PS: A client just asked for me to consider using "Comic Sands" !! Argh
(twice)!