If you can answer yes, to these questions, most things are working.
Does it boot up to the desktop you installed? Are things easily viewable?
Can you run a network application, like Firefox and get to a web site?
Can you launch an application for audio, and hear sound?
Does your printer print from an application like Open Office?
MBR - If you install a boot loader to the MBR, and the system boots, leave it alone. If the system does not boot, then this may be a source of a problem.
How do you know if Linux is working properly ?
How did you know if windbloze was working?