I was told the above information by a co-worker and believed him because he had the software and had been trying to install and use Photoshop on two computers, but I just now checked Adobe's site and it says you can install it on two computers, but only use it on one at a time, and both copies can only be used by the same person (you can't share an installation with someone). Here's the exact text:

"The activation process for individual products purchased at retail outlets supports installation on up to two computers. The Adobe product license agreement allows the primary user to install the product on a primary computer and also on a home or laptop computer for his or her use, provided that the two copies are not used simultaneously. While the activation process supports installing and activating Adobe software on two computers, use of the product on the second computer is restricted to the user who licensed the software. Allowing others to use a second copy of the software violates the product license agreement."

So, Patti, you're correct - you *can* install and easily run CS4 on two computers, but you can't run both copies at the same time. This is how I remember the old Photoshop 7 working, but I hadn't looked into it in detail until you posted your experience, so thanks for doing that.