Search an external site from wordpress.

Hey.

I’m trying to figure out a bit of a search hack.

Ideally this is what would happen:
Using a widget on my wordpress site be able to search an external site and display results as if i’d input the search query on that page (pop up new window on said page would suffice).

What I’m trying to do this for is a wordpress site that has a social component but is hosted on a seperate site running a different cms (elgg). Users will need to be able to search for members on the secondary site from the primary one.

if anyone’s got some ideas or pointers, thanks a ton.