Getting url params when serving a page

Suppose I want to link to a page, but show slightly different data depending
on some url params.  The redirecting page is NOT hosted on araneida, but
somehow needs to encode a parameter which I can then access when generating
the page so I can set an invisible field or something similar.

What would be a good way to do this?

-Jonathon
--
"I am sure that Jesus would use a command prompt.  Hello?  Ten Commandments??"