Slideshow image quality in Vista

I'm a photographer using Vista Premium 64-bit on a new PC. My WEI for
graphics is 5.9 and gaming graphics is 3.5.
I've observed a very noticable degradation in image quality, saturation and
particularly sharpness, when running images in the slideshows (the routine
that does automatic cycling of multiple images) for both the screensaver and
Photo Gallery. Sitting about 18" from the monitor, images in Photo Gallery
that are manually cycled (using the arrow keys) are 'tack' sharp. But when I
hit the 'slideshow' button, those images turn quite 'soft' (a lot less sharp)
with a bit less saturation. I used a friend's computer, also a new PC
running Vista 64, and it had the same poor quality in the slideshows. I
don't have this quality degradation on my PCs running similar slideshow
routines in XP-Pro. My images are JPGs, created with Adobe Photoshop, that
are typically approx 1600 x 1200 pixels and 700KB.
Are there any solutions?
--
Thx, Doug