Wireless sucks man. You're not going to get really good and reliable wireless without expensive pro stuff. Run a wire, they're cheap.

That said, it could be the drivers for your wireless card, it could be the wireless card itself, it could be the router. Try un-installing and then re-installing your wireless driver. Get the latest ones from the manufacturers website.

If that doesn't do it, see if there is a newer firmware for your router from that manufacturers website. If not, find someone else with wireless and get them to come to your place and see if it is slow for them. If it is, it's the router, replace it. If not, it's your wireless card or driver still.

Try a fresh install of windows to make sure wireless drivers are not corrupt if you dare, or try another wireless card. I say re-install first because you may not have access to another card and want to make sure it's not the drivers before you go dump a bunch of money into a new card you may not need.