Testing search function (in php)

Hi,

I am new to soapUI and i would like to ask what is the correct way to set up the performance test for the following scenario. I have a php webpage that sends a request to external system's ws's. And i would like to test the performance of:
1. how long does the php request take when N number of users are executing search with given parameters;
2. how long does it take for the ws to respond in this given case;

The web service part seems quite clear to me, but i would like to know how to integrate it in one test.

Thanks,
Regards,
gerda