Running another setup program

[Rebellion]

Using Installshield 2010 Premium [basic msi project]
I need to run another insatller
this is located in a subdirectory on Disk one

i.e.
Assets\setup.exe

now I've linked a Custom action from a dialog however I just cannot seem to get the Custom action correct

how do I create one [custom action] which will set the working dirctory to the correct directory on DISK1 [or even the last disk] and lauch itself

[Rebellion]

To Answer my own question.

"Behaviour and Logic -> InstallScript" section. Then click on the "Files" folder and choose "New Script File".
This will create a new script with a sample function in it.
Then add the following command into that function:
LaunchApplication(SRCDIR + "Alternative\\setup.exe", "", SRCDIR, SW_SHOW, 0, 0);
then
"Behaviour and Logic -> Custom Actions and Sequences" section.
Then right-click on "Custom Actions" and choose "New Installscript". Call your action something appropriate (eg. 'RunAltSetupAction'),
then click on it and select your function in the properties on the right.
Then
"User Interface -> Dialog" section (from the lefthand menu).
Expand the dialog you created, and choose "Behaviour". Then click on your button, and assign the "DoAction" event. Then choose the default action you created (RunAltSetupAction).

Job Done