um...i'd really really really really love to see the day the GeForce FX 5600nU can be on par with the Radeon 9600Pro
nVidia's FX 5600 is supposed to be on par with the 9600np
the 5600 Ultra and later 5600 Ultra (FC) were supposedly capable of competition with the Radeon 9600Pro
however that just isn't the case
the 5600 is an ideal choice over the 5500, as it's probably a few percent faster (THG refuses to benchmark the 9250, 9550, 5500 and 5700LE on the basis that the cards are avliable in too many different variations (Which I don't believe they are avliable in any more variations than any other mid-range segment graphics card)
looking at 3DMark2003 the GeForce FX 5600 is shown as competitive with the Radeon 9500 128MB, and about 100 pts faster than the Radeon 9600 128MB (the Radeon 9500's are faster than the 9600's, but the 9550 is slower than either (if that makes sense)
in Aquamark3 the GeForce FX 5600 is shown as competitive with the Radeon 9600SE....OUCH
in their Doom III benchmark the difference between the 9600Pro and FX 5600 means playable and unplayable, if you dropped the resolution down one setting it'd give you that 8 FPS for the 9600 to play at 30 some odd FPS
however the FX 5600 is under 20 FPS, basically it cannot play that game at that quality setting with out use of a super low res (like 320x280, which would just look godawful)
in Call of Duty the GeForce FX 5600 matches the 9600, and the 5600 Ultra matches the 9600XT, so in Call of Duty the 5600 series cards match their intentended ATI counterparts
in Battlefield Vietnam the FX 5600 Ultra is shown as competition for the 9600np, and the 5600 is unplayable
You have to remember that nVidia's launch of NV30, along with NV31 and NV34, only one card was really a succes, the NV34 FX 5200
the NV30 was too loud and ate up too much power to be practical for all users seeking a high performance part
the NV31 did not deliver enough power (the NV31 and NV34 are just cut down NV30's, but with NV31 they cut too much off for it to be a viable mid-class solution, the NV31 is what a low-range card should be)
the GeForce FX 5600XT, 5600, 5600 Ultra and 5600 Ultra (FC) cards were overall a failure, as they delivered sub-standard performance at a high cost (I believe the GeForce FX 5600 Ultra on release was $200+, and the 5600 was $150, when 5700 was launched the 5600 Ultra (now the FC version) was dropped to $100 and made a perfectly good deal)
the Radeon 9500 and 9600 series are generally better
the GeForce FX 5700 (NV36) was a huge success, as it finally gave nVidia a powerful mid-range card
the GeForce FX 5600 Ultra is comparable to the Radeon 9600np, but usually slower (it cannot hold high FPS in some situations, if a 9200 Pro existed, the 5600U would've made the perfect competition)
as to the FX 5700, the GeForce FX 5700 is comparable to the Radeon 9600Pro with no questions asked, and the 5700 Ultra/9600XT battle rages on as to which is 1% faster in which test at which settings and which system enviroment (no, i'm not getting back into this john, the 9600XT wins imo as it's the only one left for sale, easily found, and at a reasonable cost)
as to nForce and Radeon, it will work fine
I know many people who run nForce2's with Radeon 9500 and 9800 series cards (as they prefer ATI)
I run a GeForce FX and an nForce2, and have no issues with the system, but with an ATI card i'd have no issues either
I have no advantages to having the GeForce FX/nForce combination (Except when I install all my drivers, I get to see the nVidia logo about 30000 times before all is said and done (let's see, gfx driver, chipset driver, IDE driver, sound driver, SATA driver, ethernet driver...did I forget anything?)
it's really your choice between nVidia and ATI
in normal use (1 monitor, 1 graphics card) they are evenly matched, and you basically have to choose which name sounds better, and which has a part in your price range, that you like (performance wise)
I choose to use nVidia because I prefer their multi-monitor software, and because I like having nView (which makes WindowsXP sort of like Mac OS X, in that you get simmilar effects and features as far as GUI enhancements)
as to OpenGL 2.0 support, i'm not sure what ATI's big claim on that is...but iirc when the Radeon 9 series was launched OpenGL 2.0 didn't exist
and if you want to get into a pissing contest over which has the most current support
nVidia builds the only DirectX 9.0c generation part
ATI builds DirectX 9.0b generation parts (they can run 9.0c, but cannot support all of it's features)