I don't really need a better video card to play Bioshock, since it does meet the minimum requirements (barely). But the rest of my computer just barely meets Bioshock's requirements, too.
Processor:
Bioshock requirement: 2.4GHz Single Core Processor
My computer: 3.0GHz Single Core Processor
Bioshock recommended: 3.0GHz Dual Core Processor
RAM:
Bioshock requirement: 1GB
My computer: 1GB
Bioshock recommended: 2GB
Video RAM:
Bioshock requirement: 128MB
My computer: 128MB
Bioshock recommended: 512MB
Video Card:
Bioshock requirement: GeForce 6600 or faster
My computer: GeForce 6600GT
Bioshock recommended: GeForce 7900GT for DX9, GeForce 8600 for DX10
In this case the XBox 360 version would be a better way to go.