I found that the Wacom driver from HP "SP24581" HERE has been the best one that I have found. I don't have Photoshop but give it a try. I know I had problems with other programs trying to get the pressure to work and this one did the trick.
Make sure you uninstall the old Wacom drive first then reboot, Just doing a driver update does not always work right.
HP Compaq TC1100 | Intel Pentium M 1.2Ghz | 2 GB PC2700-333Mhz | NVIDIA 420 Go 32MB | 120GB HDD | Broadcom BCM43222 wireless N card| Windows 7 Ultimate x86