I had a system almost identical to yours with the exception of a 7900 series card (actually about equal to an 8600GT due to having twice the memory bus width, 256bit vs 128bit for the 8600)
I built a Dual monitor passively polarized system
http://mtbs3d.com/phpBB/viewtopic.php?t=136 :
http://picasaweb.google.com/nubie07/StereoMonitorStand
This uses some polarized glasses ($3) and a half-mirror (see a local glass shop) with two LCD screens. This is a million times better than the Edimens on a CRT (I sold my E-dims on ebay a week after I got them they were so crap.)
The main problems are you will need a second screen and a mounting system, but it is totally awesome. (And it needs to be polarized at 45° or 135°, or use a polarizing filter on top of the screen to rotate the polarization)
Basically I wouldn't get a GTX either, I would pick up a 7900GT or 7950GT 512MB on ebay (~$130-150), or a 7900GS (~$70-90), and you won't see much of a difference in performance from your 8600 card (AFAIK). If the price is the same a 7900GTX is fine too, they are all the same chip (the GS has less shaders, the same as a 7800, but is the smaller chip process and can overclock to the same speed as a GT/GTX with good cooling.)
7900gt 512mb on ebay
7950gt 512mb on ebay
Just a thought. I would try a few different types, this type can be tried with any simple mirror and any secondary screen (CRT, smaller LCD etc), while sitting on a desk.
http://www.crystalcanyons.net/pages/Tec ... ewing.shtm
Buy some anaglyph glasses and linear polarized glasses from berezin.com for $10 just to check out those options, you will easily see what is going on, you can also try the polarized setup on a desk without any mounts:
http://picasaweb.google.com/nubie07/3DMonitor
So there are a couple options for you. Welcome to the wacky world of S3D

_________________CAVE, see what all the fuss is about:
http://www.youtube.com/watch?v=N6NN5JKlIi0