You can get a retail X1900XT Sapphire for $475 off newegg, so it's 175 dollars more. And the difference between the X1800/7800 is noticable. If you have the money go for the X1900XT.
The X1800 performs around the 7900 GT. The X1900 has around 23 more frames then the 7900GT, so you can see the improvement, it is almost the same performance as SLI 7900GT's. (This is in BF2 w/ 12x10 res with 4x AA)
The MSI would be easier to set up if you don't know everything about the BIOS.