Chklin, I'm curious about why you're so confident that that XFX card will work in the 540S. The box wants you to have a 350W power supply. I installed the card on my 540S and things seemed to be going well, until I decided to access the DVD burner. That's when the computer shut itself off. When I turned it back on, the DVD burner was broken.
I just replaced the DVD burner, but, obviously, the 9500 GT is no longer an option for me. Maybe a safer card like the ATI 3450 or 4550 or ... possibly... 3650? Not sure. Let me know what you think.
Also, under load my fans take off to max RPM's (5000 or so) and sound like a vacuum cleaner. Very annoying. I'm curious why your system seems quieter. Maybe because you have a discreet video card.
That's terrible that the video card + DVD burner apparently caused your PSU to be overtaxed. The 3650 seems like a good option and I've heard it's faster than a 4550. But unlike the 4550, is the 3650 available in the LP format? I couldn't find such a card on Newegg's site.