Hi there!!
I am new to arduino and have been experimenting with it for a bit now. I wanted to have a motion sensor which detects if someone was there and then would be able to display a shape. More than one person would display different shapes.
Any links provided on similar projects/examples would be really helpful.
Thanks in advance 
Passive Infrared Sensors can be used to detect the presence of (actually, motion of) warm bodies.
However, they have no capability to display a shape. Nor can they tell how many warm bodies are present.
For that matter, an Arduino can not display a shape, either.
You need to tell us a little more about what you are trying to do...
ok sure. Basically I wanted the arduino to have a motion detection attached to it. If it detects someone then it will display a shape on the monitor.
I am just not entirely sure how I would go about getting everything together.
thanks for the reply.
As PaulS says motion detection can use Passive InfraRed (PIR) sensors, to detect warm body motion. Detecting several different warm bodies is harder.
Alternatives include ultrasonic measurement, but that is likely more complex as a starting point. A radically different approach is a simple video camera, e.g. a webcam, and some simple image processing, maybe OpenCV, running on a PC. Not an Arduino solution, I accept.
Lots of the 'modern' room 'air-fresheners' contain PIR sensors. They also contain a solenoid which you could use to move a shape
Have a look at these as examples:
http://www.rapidonline.com/Electronic-Components/Sensors/Pir-Sensors/Omnidirectional-pyroelectric-PIR-sensor-TO-5/81561/kw/PIR
http://www.rapidonline.com/Electronic-Components/Sensors/Pir-Sensors/General-purpose-pyroelectric-PIR-sensor-TO-5/81559/kw/PIR
Googling for PIR circuits threw up lots of resources too. The ones I glanced at looked more complex than you need because they are self-contained alarms, and you don't need the extra's. So it may be simpler than you think.
HTH
GB-)
Thanks for the reply
Your suggestion about the webcam seems like a good starting point. I will do more research on this. Any examples you know would be welcome thanks again!!
For PIR I just googled fo "PIR Arduino" and got this link and this link. The second link looked relevant as he was using multiple PR detectors.
For Webcam and motion detection. If you have a good library, or bookshop, have a look at this book
Or google its forums.
I haven't used it (just read bits of the book and manual), but motion detection looked straightforward, and I think there may be some face detection stuff in there.
HTH
GB