Creating Joomla (1.5) users from a c# Frontend

I have been developing a tool at my work, I developed this in response to our very monotonous new start process.

The new start process involves creating an AD account on up to 3 separate domains, creating a mailbox, and creating an account on one of our online systems (which is powered by Joomla 1.5). I have created a Frontend in C#, it creates all the ActiveDirectory accounts just fine, but now I am trying to find a way to have it send the data from the form to our Joomla system to create a user.

I found the following documentation on creating users within Joomla: http://ift.tt/2oXSypq

as well as the COM_User documentation, however, web development is one of my weaker points and I'm stuck on the implementation of this. The person who looks after the Joomla server said he will upload any files i need to make this happen, the only issue is I'm not sure what file that would be. Would I POST the data to some javascript file I create that executes the user creation?

What would this user creation look like on Joomla side? (keeping in mind it being 1.5)