I'm going to start this one by saying you really shouldn't be gaming on a wireless network. I love WiFi. I do. Everything I own is connected to my wireless network. When I don't have WiFi I have my data dongle so I'm never stuck without something to do.
But the same way friends don't let friends drink and drive - gamers shouldn't let team mates play on a wireless connection. What an ethernet cable lacks in freedom it more than makes up for in stability and speed. WiFi networks can face interference and are just generally slower.
I used to have a wireless mouse before I got myself the deathadder for the same reason. It was handy and easy to use but those small delays really do start to add up.
If you can reach your router from your desktop then get a cable in it. Your ping will be better and you won't have to deal with wireless stability issues. Trust me, you'll be thankful you did. I have a great big ugly cable but I only use it when I'm actually gaming. Normally I just have the WiFi on and I connect it from behind the PC before starting. You'd think I'd forget but you soon notice the ping difference when you're used to an ethernet connection.
If there really is no way to reach your router and moving the desktop isn't an option (yes - it would be worth it) consider getting a better wireless card. You don't want an internal adapter because it can't get a good signal that close to the motherboard and burried inside the case. Ideally something high powered with an external antenna. You also want to use a decent router with at least one (ideally more) external wireless antennas. If you can attach a directional one point it in towards your gaming PC with as little obstruction as possible.
In my case I still like a strong signal to my router when I'm not gaming and I can't change my router because my ISP rules are pretty strict. So I use a third party device called a standalone WiFi booster it gets plugged in at the half way point between the gaming PC and the router and boosts the WiFi signal between them. I still wouldn't game on it (though if I couldn't reach the cable I would) but it more than doubles the strength of my signal and I've not had a problem with reliability so far.