U2412M IPS functionality

Just received my U2412M monitor and it is amazing!  The only problem I'm having is figuring out how to get the landscape view - to - portrait view switching to work.  I have downloaded the update for my ATI graphics card but when I click on one of the rotation mode settings on the "Rotation" tab in the advanced screen setting box (or the ATI taskbar menu) I get the following:

"The requested Rotation mode is not supported by your current display mode (resolution and/or refresh rate and/or colour depth).  Please change the current display mode and try again."

(I have a Dell Dimension E510 running XP with an ATI Radeon X300 SE 128MB graphics card.)

I found a side-comment in one of the other posts that IPS functionality is driven by PowerNap.  When I loaded the driver from the CD I read through the description of PowerNap in the operation instructions and, like Chris, decided the normal Dell power management was fine - seems like the fact that you need PowerNap to drive the IPS functionality should be mentioned somewhere!!!  I went back and installed PowerNap but it does not seem to have changed anything in my options for switching to portrait mode.  I suspect this is an IBM issue (idiot behind machine), but I'll suck it up and ask for advice anyway...

Thanks,

JRC