The preliminary screen will be done by the HR group, who will likely go over your resume. An initial screen is done by the hiring manager for the department you'll be working under, which may or may not contain technical questions. They may ask what position you'd like to apply for if you didn't specify in your initial application. If you pass this initial screen, you'll be passed on to the manager or a co-worker of the respective group, which will then go into more specific software questions.
For me, the questions consisted of general software knowledge , as well as some software problems. If everything goes well, you'll be hired.