There is a difference between pci and pci-e. you do NOT want a pci video card.
You also do not want to assume anything. Your computer may not even have a video card expansion slot, so you need to carefully check your system specifications before buying anything.
Also, a 375 watt power supply may not be enough. Many of the newer video cards require more than 400 or 450w. For comparison, I've read that the newest 8800 series video cards draw over 300 watts just for the video card alone.