syntax for running system commands

Just wondering if anyone know what the syntax is for running a system command from within a VB program (for instance, say I want to run the program blah.exe from within my VB program . . . how would i go about doing this?)

Also, anyone know how to make a dialog system modal (like in VC++ where the user cannot use other programs without first finishing with the system modal program. . . for instance, if i wanted to write a password app and didn't want the user to be able to use any other programs without first entering the correct password and kiling the dialog...
Regards

1)Use Shell() for executing any exe program

2)Open the form with vbModal as a parameter
E.g.: form.open vbModal.

vbModal is one of the intrinsic VB enumerated constants

Hope that helps

al_paso