I'd just like to confirm I've experienced the same thing. Happening on any
jpeg files sent to our pc users.

Our macs all a

Mac OS: 10.4.11
Photoshop 10.0.1
Entourage 11.3.6

PC users are all Win XP service pack 2 installed and automatic updates
turned on. Same behavior as original poster, when a PC user tries to open the
file they see cannot display preview.