Order Form Template: php script possible?

[shout]

I'm creating a custom Order Form template and I'm finally starting to understand the internal API.

 

However, I'd like to run the <b> domainid</b> function to get WHOIS data on a domain--and I'd like to be able to do this through Ajax. I created a script "whois.php" and put it in my template folder, but I can't figure out what the URL of it would be. It would need to be a standalone PHP file and not a .tpl file, because the .tpl files return tons of HTML and stuff, I just want a minimal yes/no sort of answer.

 

Has anyone done custom Ajax before, and if so, how do you do it? How do you define a URL to the PHP?