Linksys makes good wireless gear, yes. These devices also support the 5GHz band, meaning that you have a good chance of getting an interference-free network. And yes, an AP is what you want when you already have a router.
I just picked a PCI wireless adapter for you, but something else may suit your needs better. For a laptop an USB or a PCMCIA device is needed insteadof PCI. For a desktop, an USB adapter may be placed more favourably to get a better signal.