Before you tinker with "alternative antennas" on the PCI card, try plugging a USB WiFi into a USB extension cable, and move it around a bit to see what signal you get. My daughter thought she was going to need an RJ45 cable from her study to the lounge (other end of the house), until an RF "sweet spot" was found.
The USB WiFi hides behind a picture on the wall, and gives four out of five bars.