Yes it works great

In our lab we have 3 machines setup with Parhelia cards.  They have XP1400, XP2600 and XP3000 processors, with a gig of RAM each.  On the 2600 and 3000 using triple-screen output on FS2004 we get smooth-enough framerates (30+) at 3072x768x32 resolution.  These are the 256mb Parhelias.

It's not sky high, but that is with photoreal custom textures and all texture and terrain detail settings maxxed out (we use a view distance 60nm, cloud draw 50nm, and 3d-detailed clouds on full)... Obviously it goes up and down a bit with the weather settings.  We also don't use autogen, although the impact of turning it on is not appreciable (we just don't like the cartoon trees and buildings it drops over our pretty textures!!)

Overall they seem to be excellent cards.  I'm not mad keen on the antialiasing, but the settings for it are quite intricate so I am not sure if I have it set right (and I'm only bothered by it when looking at a very large projected front view - on a 17inch lcd it is tolerable).