Software Deployment

I am using installshield 2008 basic msi.

I basically have a service which depends on another service and this service only exists on Vista.

I thought I would use the reg.exe to create the registry file, for dependencies, this works perfectly when I run from command line manually, but in installshield it just doesn't do anything no errors nothing.

My custom action is new EXE > Path refering to a directory

Working dir: WindowsFolder
Filename and commandline: add HKLM\system\currentcontrolset\services\myservice /v DependsOnService /t REG_MULTI_SZ /d WinHTTPAutoProxySvc\0 "[SystemFolder]reg.exe"
Return Processing: Synchronous (Ignores exit code)
In-script Execution: Deferred Execution in System Context
Install Exec Sequence: After InstallFiles
Install Exec Condition: Not Installed.

Any better ways to do this or get the reg.exe to create the registry?

Thanks in advance