Q: How to Photo Stream in iPhoto

Open iPhoto, go to iPhoto > About iPhoto. What version? Are you logged into iCloud in System Preferences > iCloud, and is Photo Stream on there?

for set up instructions see - http://www.apple.com/icloud/setup/

for FAQ and links to trouble shooting - http://support.apple.com/kb/HT4486

LN

"If you installed iPhoto from the iLife ʼ11 DVD, or if it was preinstalled on your computer along with OS X Snow Leopard v10.6.8 (or earlier), you can update iPhoto with Software Update (choose Software Update from the Apple () menu)."

I have iPhoto 09.

So, why can't I photostream?

Because as your post explains and as the links I sent explain - you must have iPhoto '11 to use Photo Stream

LN