Anyone who says playing an mmo with a wireless setup isn't advisable must have had some horrible adapters and/or routers, or possibly terrible ISP. I've never had any wireless problems whether it be laptop or usb adapter. My latency while playing wow hovers around 55-65ms and that's while on Verizon DSL. Now before anyone nerdrages, I know a wired connection will always be 'optimal' compared to wireless (3 years of hardware and networking courses and even more independent study, not bragging but I know what I'm talking about), but to say in general that wireless "fails" is flat out wrong.
If you want to play wired try to get your router as close as possible to your pc and get as long of an Ethernet cord as you can/need (as stated by others). Before you even think about drilling though, try a *new* usb adapter.
you may have a point. Wired is by far priemier when it comes to online gaming. The new "N" routers are the best for wireless gaming within a certain proximity, again subject to layout, obstacles,etc. Although I am no expert when it comes to this, I would believe that with the new "N" band, wireless has come a long way.
Again, with that being said, FFXIV has zero tolerance for packet loss, (so I have read, and seem to experience). This, alone, makes wireless a terrible idea, IMHO.