Print Picture with date

I don't believe that the XTi will let you have the date on the picture.
Easiest solution I can think of is to download some free software like Paint.net and use the text tool to add it in the corner before printing.
If you have forgotten the date or time, and you're using windows (not sure how to do this on a mac) right click on the image, go to properties, click the summary tab, and then click Advanced. That will give you something called the EXIF data, or all the info about the picture (camera model, shutter speed, etc). Near the bottom should be the date and time.