How do I run an xxx.msi file?

I have a need to run a series of msi files in a pended fashion. I have a function that allows me to run exe's that way (runs a.exe and when it ends, run b.exe). My function works fine for exe files but nops when trying to run an msi. My function uses:

Private Declare Function OpenProcess Lib "kernel32" _
(ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
ByVal dwProcessId As Long) As Long

Any way to get an msi file to run too? Basically I'm building an an installer program which has to run a mix of exe & msi files.