You could call the install from a vbscript with encrypted credentials, so it runs the installation with those credentials. Alternatively you can encrypt or compile the vbscript to protect the credentials.
From the vbscript you could run the following command line
MSIEXEC.EXE /i yourmsihere.msi /qb! /lv %Windir%\temp\yourlog.txt
Note that the /qb! switch provides a very basic interface without a cancel option, so the user sees that something is happening. if you want a complete silent install, then you need the /qn switch.
I have attached a quick sample script (remember to rename to .vbs), that should point you in the right direction. Use at your own risk.
You might also want to include code to check the software is already installed so it does not install over and over.
Hope this helps