I started playing it on a AthlonXP 2500+ (barton core), XFX GF 6800, 1GB ram.
I could play at nearly max detail, and a decent res (1024x768 or 1280x960)
I noticed a massive difference in FPS when going from 1GB to 2GB.
The FPS was smooth, but "choppy". Was easy to tell it was because the system was having to read from HD. I noticed this most easily at the part where the evacuation was happening and tons of people were on screen.
2GB system memory is definitely a a huge must.
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Just bought me a new system:
AMD X2 AM2 6000+
EVGA GF 8800GTS Superclocked
2GB Kingston HyperX RAM 3-3-3-10
ASUS M2N32-SLI Deluxe (w/ wireless) nForce 590 SLI chipset
2X 500GB Seagate SATA2 HD's NCQ 16MBcache (going into a striping config)
Unfortunately the ram and optical drive were placed on back order, so it's not up and running yet

Might have to get a bigger PSU as well... Bought an Antec Sonata III case that came with an Earthwatts 500watt PSU, hope it will be enough.
That being said I should probably actually look into the wattage of all my gear to be sure.
Think I gonna sell the vid card right away though and get a 8800GTX instead.
Playing Juarez in DX10 will be a bit smoother then.