Recently i met customer problem where NAV 2009 SP1 components didn't work after "correct installation".
Problem is: customer installs NAV 2009 SP1 components by run msi file - for example "Microsoft Dynamics NAV SDK.msi". But this way doesn't install "Prerequisite Components" needed by NAV 2009 SP1. And it could be these installed NAV components will not work (because it missing prerequisites).
Only supported way to Install NAV 2009 SP1 components is - run "setup.exe".
However "setup.exe" will uninstall previous NAV version and installs new NAV 2009 SP1 version. If you need to have few NAV version installed - you need to run msi (instead of setup.exe).
So conclusion: both ways have it strength and weakness. You can choose what you want, just you need to know about possible issues...
Gedas Busniauskas (gediminb)
Microsoft Customer Service and Support (CSS) EMEA