It was the RGB settings but not where I thought -
I had to specify BOTH Windows and PhotoShop to use the right colorspace.
in Windows (I'm in Vista so this may be different for you):
- goto Start/Control Panel/Color Management
- make the sRGB Color Space Profile.icm default
- goto Edit/Color Settings
- under RGB select Adobe RGB (1998)
Everything looks great now - PS and Irfan display images very close to the same and that's what I need. I use Irfan to view pictures because it's very fast, I use PS to edit them though and the 2 programs need to display the same for that to work.