Hi,
The simplest way to do this might be by setting up a simple load test in SoapUI:
So, just set:
1 thread
Strategy: Simple
Limit: 100 Total Runs
Optionally add a short Test Delay, otherwise your service could get too much load.
Another option would be to use Groovy TestSteps to loop over your Request TestStep 100 times, this is easier than it sounds, but would require simple coding skills. We can talk more about this if you want. There are plenty of examples of Groovy script looping on this forum - heres one example http://community.smartbear.com/t5/SoapUI-Open-Source/Looping-series-of-test-step-using-groovy/m-p/102994#M18035
To run from a DOS prompt, there are many options e.g. Maven, Gradle scripts - probably the simplest option is to use the testrunner.bat script provided in <SoapUI Home>/bin - see https://www.soapui.org/test-automation/running-functional-tests.html
Again there are many community posts on running SoapUI from scripts!
Hope this helps,
Cheers,
Rupert