My friend has a Dell Inspiron with a ATI "X1400" card in it. The card has a high number yet it performs like ass. A x850 pro will piss all over it in benchmarks. Be wary of numbers. Nvidia does that too with the 7300 seeming to suck.
In general ATI & nVidia usually trade blow for blow depending on the games that are being benchmarked. nVidia's mainstream and value cards are generally better than ATI, the GeForce 7600GT is a good example of a mainstream card with very good performance.
ATI's cards tends to be better when you look at their high end cards like the Radeon X1900XT and X1900XTX. Their X1800XT is comparable to the GeForce 7900GT. People generally say that the graphics quality of ATI's video cards are better than nVidia because graphics "look better on screen."
ATI cards do consume more power though. For example, an overclocked 7900GT 256MB eats up about 58w of power. The X1800XT 256MB eats up around 104w of power. You're talking about a difference of 46w or 80%. Therefore, you will need to buy a slightly more powerful PSU for an ATI, than you would for a nVidia. The cost in electricity will not kill you.
Regarding a PSU, don't be cheap. Many people want to spend as much as they can on a CPU and GPU, but when it comes to the PSU they want to spend as little as possible. Bad idea. If your PSU dies, well let's just say that PSUs don't really like to go to Hardware Heaven alone.
Buy a PSU from a good namebrand. I prefer the Seasonic S12 series because they are have been in business for a long time and they design PSUs for both the consumer market and industrial market. More importantly, their PSUs have been tested by independant hardware sites and have gotten good reviews across the board.
The S12 series is very quiet; I can hear the other fans in my case, but not the Seasonic. Their PSU are aslo very efficient (85%), meaning it doesn't waste too much electricity from the A/C outlet to power up your PC. However, the Seasonic S12 series is somewhat expensive ranging from around $55 for the Seasonic S12 330w PSU to $160 for the Seasonic S12 600w. You get a rocksolid PSU for your money.
Other namebrands that you should consider are Antec, Enermax, Fortron, OCZ, and Silverstone.
The RADEON X1600-series is expected to substitute RADEON X700 family of graphics chips as well as to replace the RADEON X800 GT and possibly the RADEON X800 XL (or GTO2) products from performance mainstream segment. The obvious advantage the RADEON X1600 has over predecessors is support for Shader Model 3.0, HDR and some other technologies. The probably disadvantage is 128-bit memory bus as well as pretty low texel-rate. We will find out the outcome later in the article, but now let’s summarize everything we know about the RADEON X1600 also known as RV530, based on the results in synthetic investigation.
which manufacturers the best? ASUS,PowerColor or Sapphire? can support by my board..... gaming n other...
I would go with the X1600XT since it is the fastest model. I don't think 256MB or 512MB will matter much for the X1600 series because it is not fast enough to put that extra 256mb to good use. It's more about marketing.
The ones you listed are good. I think Sapphire tends to be the least expensive, but they also only have a 1 year warranty.
Asus sells great quality parts and will probably be the most expensive of the three, but not by much. Last time I've checked, they offer a 3 year warranty.
By all means, check Cleeve's "Short List" on this very forum (it's the first sticky or so).
If you're buying a single video card (non-SLI/Crossfire), which I reccomend, then you don't need to buy a separate Power Supply, as some cases (not all of them!) have already a very reliable one. Try to find the Antec Sonatta II. You can save some precious money that way.