XML query of 3rd party site during registration

[kermittf]

I was wondering if anyone knew of a plugin/extension/module that would allow an XML query of a 3rd-party site during registration?
Even if something was close, then I could mod it to fit (calling the other site/changing XML params/etc).

I have the ability to query another site for the entered username. What I envision is if the query returns good data, then registration continues with the email confirmation/etc. If the query returns an error, then the registration barfs and they have to either enter correct info, or just dump them off to another site/page.

If I could get this working, then that wretched captcha could be s*&^-canned, as only valid people could create accounts.

Any advice/URLs are appreciated.
Jim