How to handle Java script onload() function in selenium IDE/RC?

I am doing automation in selenium Python unit testing frame
work.

I am facing the problem like in my web product,there was a
page with search functionality, when searching some records it will open a
confirmation dialogue window with OK and CANCEL buttons. But every time we didn’t
get this dialogue box, only when display records more then 500 , it will show
this message" More than 500 matching records were found. Search may take a
few minutes to complete. Do you want to proceed?" selenium was unable to
handle this Java script onload() function.

I applied the below functions:
1. sel.get_confirmation().

Is there any solution or alternative for the above issue in
selenium IDE or RC. Please help me to solve this issue. Please look at the attached screen shot for web page reference.

Thanking you in advance
Raghavan.