I understand you want to automate the process, but the more information you can provide, we can then provide a suitable solution if possible.
- I don't understand why you would want to launch TestComplete using different credentials.
- Is it not possible to run two testcases within TestComplete.
- I still don't fully understand what your batch file is supposed to do, apart from calling a test in TestComplete.
If it's a console application, then you can read the output using either Sys.OleObject("WScript.Shell") or what Bonibom has mentioned. If it's a windows application that doesn't produce any standard output, then it can't be done. Or you can use Tested Applications. For command line arguments, see TestComplete Command Line