I'd go with the PCI card, if you can stomach opening the case and plugging a card to the motherboard. It won't occupy a USB port, and you'll probably get better speed. Look for an 802.11g card. Something like
this.
Is the PC within cable distance of the APE? I can't remember if the APE has ethernet ports (maybe 1?), but if the PC has a network interface, that might be a cheap solution.