Registry check in logon script

Hi,

We have group policy which adds registry value to HKCU and powershell script as logon script. Problem is that logon script starts before registry is updated.

I need some advice how to check registry using powershell. Timer or something in the beginning of the logon script and script goes on when registry value is ok. Maybe something like below? 

Logon.ps1:

-------------------------------------------------------------------

do
         check registry
while

script continues....

-------------------------------------------------------------------

I'm quite rookie so i need rookie compatible advice :)

Thanks

~ Jukka ~