Help: Loadtest with multi-user!

Hi!
I met problem with loadtest by SOAPUI with multi-user, someone please help me, i'm a newbie with this tool
Background:
testSuite: POS
testCase: ----LOGIN
testStep: ----------getHomeJsessionId
--------------------getSsoStoreLogin
--------------------getAccountStoreLogin
--------------------postStoreLogin
--------------------getPrepaidCardList
--------------------getEealletServiceGetCurrentBalance
--------------------postBuyAirtimeCardMOBI
--------------------postInqueryAirtime
--------------------grrovyScript: Checker
--------------------getLogOutHTML
With 1 user, i can loadtest with 1 thread. However I increased thread to 10, soapUI -> created 10 virtural user, sure loadtest will faill because: only use 1 username/password x 10 -> authentication failed. So i created 9 another users, but i don't know how to input 1 username/password to 1 thread. I loadtest with 10 threads/10 different user at the same time.

Thanks!