John, I don't think you really needed a Speedlite in this situation. Using 1/50 sec, as mentioned by JP, is the issue. You didn't need to shoot at 1/50 - you had a couple of options without using flash.
1. You could have opened the aperture from F2.8 to F1.8 to allow more light in (though you would have ended up with a very narrow depth of field) - this would have allowed you to increase the shutter speed, but F2.8 is probably about right for this type of shot;
2. You shot at ISO 200, I'm not sure how the 450D handles noise at higher ISO but you could have increased this to 400 or 800 without much of a problem (I used to have a 400D), and this would have allowed a shutter speed of 1/125 sec or faster (which would have eliminated any camera shake or motion blur). It may be a bit grainy, but it's better to have a bit of noise and a sharp image (and you can reduce noise in PP).
If you are not comfortable adjusting aperture/shutter speed/ISO, you could try one of the semi-auto modes with auto ISO and let the camera work out what settings need to be adjusted. Review the EXIF data/settings afterwards to get a feel for what settings are needed for different situations.
As for the flash, I don't mean to sound patronising, but I'd leave this for now until you have the basics worked out.
As an example of using higher ISO, this was shot on Saturday at ISO 500, F2.8 and 1/320 sec (which was probably quicker than I needed but although he looks like he's sat still I was actually following him around the room from low light at one end to near a large window - he's halfway in this shot).
IMG_5473v3 by
Ian J Bradshaw, on Flickr
Keep practicing and posting up your shots, plenty of people to offer advice on here.