softcris: I'd recommend an nVidia 8500, 8600 or 8800 series graphics card. The 8600 series is fast enough, while still affordable: a 8600GT based graphics card with 256 Mb of memory can be had for less than € 100,-
You could step down to 8500GT based graphics cards (around € 80).
The 8400 series is too slow. Cheap, sure, but too slow for serious 3D hobbying. You're better off with a 7300GT based card - same price range, but significantly faster.
The nVidia 6xxx range is almost phased out, except for the 6200 - very cheap graphics cards for non-3D work.
THe 7xxx range is also almost phased out. A shame, the 7xxx series had some very nice cards (7800GTX, 7900, 7950GX2).
The advantage of the 8xxx series graphics card over the older 7xxx and 6xxx series is not directly apparent. But it does have advantages. 

• DirectX 10 enabled
• Highly programmable - you can use the graphics card as if it were a CPU. Seen that at Siggraph this year, yummie!

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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