Yes flash photography takes it to a whole new level when shooting if done correctly. If you want to make the image not look like a flash image, it will take lots of practice.
If you just want the picture to come out, sharp and clear, leave it on auto and set the flash to P-TTL. I have the Sigma 530gt Super which is almost the same as your flash but it is a little bit more powerful. On auto, the flash is able to do a great job in capturing the picture. You may get that "flash" look where the face is pale and the background maybe dark but the exposure will be correct.
I would check out where the event will be taken place. If the ceiling is not so tall and if it is white, you may want to experiment with bouncing the flash like what Ash mentioned.
If the lighting condition is dark and constant you may want to set the camera and flash in manual mode. Check out this video made by a member on this board. He teaches you how to shoot in a nightclub/bar but it can be used in any room that is dark. It may be too advance for you but you might want to experiment with the techniques.
YouTube - K10D: Bar/Nightclub photography tips PART 1
Here is another link that I just found posted by a member here. Lots of great newbie info here
http://www.pentaxuser.co.uk/forum/topic/Digital-SLR-and-PTTL-flash-guide-4323