Ihave a canon pixma iP6000D want to mirror image

In the printer driver settings, where you can select the paper type, you have to choose "other paper" and select "T-Shirt Transfer".

Of course; usually it's a matter of having the application (e.g. going via Inkscape or Adobe CS4) print that design mirrored L-R, though it's possible that Print Mirrored is available in the printer driver also. If you mirror it both places of course, it will look unmirrored (i.e. raw/unripped.)
You probably want to use some good UV stable inks and a 6-color (plus black) printer rather than the MP600 (whose ColorLife inks are for paper) if you can, because the colors will be more accurate and compatible with your plastic transfer media so the shirt will look great longer. Then again, you may not want to spend more than it would take to have an embroiderer make 1000 shirts, onesies, dresses, and skirts.

If you are printing text only, you can create it using wordart in word and then use rotate or flip command to reverse the text.
If you are printing a JPG with text, the easiest way will be to use photoshop to edit the image and add text if desired, then use the mirror utility, The picture and text get reversed and the transfer is printed in reverse to become "positive" when you iron it on the Tshirt.

hope this helps.

I print reverse images (in Word) for t-shirt transfers by going into the printer properties. Select the "Main" tab and for Media Type select "T-shirt Transfers." I believe that it prints the mirror image by default.

There isn't a selection for mirror image, however, if you select "t-shirt transfer" in the printer properties, it will automatically print it as a mirror image, ready for transfer.

Check in your settings for media type (plain paper, photo paper, etc.) and see if there is a T-Shirt Transfer media type. If not, you may need to use a graphics editing program that has an option to "flip horizontally" before you actually send it to the printer.

Check this page and the Flip (Mirror) Image instructions by adjusting the printer settings, which are standard for most printers:
http://209.85.229.132/search?q=cache:rl2zPOnbgzEJ:clothing-design.suite101.com/article.cfm/how_to_design_and_print_your_own_tshirts+programs+that+allow+to+create+mirror+image+tranfer&cd=3&hl=pt-PT&ct=clnk&gl=pt

Download the manual for the MP 620  instruction. 
780 and 620 models use second link and look up  your own.
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=SupportDetailTabAct&fcategoryid=238&modelid=15483#DownloadDetailAct


http://www.usa.canon.com/consumer/controller?act=SupportIndexAct

try to print as T-Shirt transfer - the printer automatically mirrors the printout then

I called a Canon rep and the printer does not have that option on it.