So you've got a photo with a weird date on it - how do you change it? Well on OSX or Linux you can do it the terminal using a handy utility called exif (which you'll need to get from macports or apt):
exif --tag 0x9003 --ifd='EXIF' --set-value='2012:10:17 16:30:37' myphoto.jpg
It will create a new file with the new date called myphoto.jpg.modified.jpg which you can then rename to the original or something else.
There are of course other tools but this one works for me. I'll list others if/when I come across them.
Note: In theory you could use iPhoto on OSX but it is unfortunately buggy - so if you have a date like 1/2/1911 and you try moving it forward with iPhoto then it sets a date earlier in time?!