Hi Carlosa,
Welcome to SimV or the nuthouse as many around here call it

I find it to be a friendly, knowledgeable and helpful bunch of people and hopefully you will come to know us the same ...
As for your question: I would way the best graphics card you can afford, if possible a Nvidia 8800 or 9800 series. Maybe even a GTX280 or better (285 or 295 - but those cost a lot of money!).
We just can't really tell 'what is best', as FS9 likes a combination of rather high-end components (processor - memory - graphics card - hard drive - power supply etc).
And the choice of your card also depends on if you have a PCIe or an AGP slot on your motherboard. If you have an old machine (5+ years old like mine) then you probably will have an AGP slot and for those it is rather hard to find a new graphics card anymore. If you have a 'new' machine, then you will probably have a PCIe slot on your motherboard and all modern graphics card will fit in that.
A new and good graphics card will help but if you have a slow processor or little RAM then Flight Simulator will not run very good.
And you should also look after your Windows installation. Windows can be tuned to run Flight Simulator like a charm. But that requires A LOT of patience, blood, sweat and tears ...
As a reference look at my (5 year old) system specs ... this machine will run Flight Simulator 2004 pretty nice.
If you need anything ... just let me know
