It might be tempting to schedule the ResolveSource action, but ResolveSource actually requires that the original installation source is available whenever it is called. If your installer package is authored correctly, source must only be resolve in cases where the original RTM files are missing or during some patch uninstall scenarios.
Windows Installer custom actions that launch executables (base custom action type msidbCustomActionTypeExe, 0x2) are typically bad and should be avoided. How are they bad? Let the Windows Installer team count the ways.
During internal audits we question any EXE custom actions (CAs) but inevitably some make it into the product.
You asked. We answered. One source of problems for Visual Studio 2005 Service Pack 1 was that VS 2005 SP1 targeted multiple products, and if you had multiple target products installed – most commonly Visual Studio 2005 and SQL Server 2005 that uses our IDE –