A dual core processor will make your renders many times faster than your current machine, at the same quality.  With bigger processor + memory, you can also think about rendering at much higher quality, or more complex scenes, or both.

No graphics card will shorten your render times, but it will make moving around in the Preview much more comfortable, and can show you higher resolution with comfortable speed; be aware that Louguet here has tested SLI (two graphics cards in the same box) configurations and he has found no real benefit even for that, so avoid SLI configs.

A newer model video card will probably improve some parts of Vue preview, and will definitely improve Poser previews.

Some French vendors that sell Core 2 Duo PCs that are below 1,000€ :
prixdunet  - I have no information on GrosBill computers, but Acer is OK (cheapest of these).  They are not famous for high quality but they are inexpensive...

keloo.fr - Packard Bell is about the same quality as Acer, cheapest choice

clubic.com - Acer cheapest again on this list

Hope this helps!  Note that I am very sure you can get better prices/higher quality than these, this is just what I can puzzle out, I don't speak or read Français.

PS:  I don't think VAT is included for any of these prices.

edit - .... uh, you ARE in France, right?  Or Belgium?

My Freebies