Go to this link: http://dev.depeuter.org/metacreations_fix_30.php#COMMENTS
Be sure to read the comments under the install instructions to tweak the steps for Win7. I am running win7 64 bit with 9 Gb RAM with no problems after running his script. There is no need to cripple your system by pulling ram, or going through the hassel of making a seperate boot sequence.
This script works by giving the memory checker in Painter what it wants to see. After that it allows the program to start normally, and all systems (including as much memory as Painter can use) will be available.
I also use a Cintiq, and have had no problems using that either, all are playing nicely together.
This is the answer provided by a programmer many moons ago. He has written a generic update that will apply to all versions of Painter up through X, and also other programs with the same problem. Be sure to use the one on the linked page (3.0) and not the earlier ones.
Thanks to Fes for jogging my memory. I used this to get Painter 4 up and running on a XP system years ago, and had forgotten it.