Well the 9800Pro uses an AGP, while the X700Pro uses PCI-E.
X700 Pro - 425Mhz Core, 700Mhz Memory, GDDR3, 8 Pipelines, 128-Bit, 256MB, OpenGL 2.0, $129
9800 Pro - 380Mhz Core, 680Mhz Memory, DDR, 8 Pipelines, 256-Bit, 128MB, OpenGL 1.5, $104.
I would go with the X700 Pro, as long as you have a PCI-E slot.