Slow WiFi Connection

Hi,

I have a Macbook Pro from mid 2010, a Macbook Pro 2008 and a PC.
My problem I have lately is with my Macbook Pro mid 2010.
It has always been a bit slow in general (beach ball coming quite often when only Safari is open etc..) so I brought it to the apple store in October 2011 (under guarantee which ended in November 2011)
They couldn't find any particular fault with the hard drive or anything else.

Now, it's been a week that my wireless connection is VERY slow. Pages load at a ridiculous speed and sometimes never load at all.
I found that it works better if I turn the Airport off and on again. But it does work just for a little while then I have to do it again and again.
I tried different browser, the same is happening.

The problem isn't coming from the router as it works super well on the PC or the old Macbook Pro.
I've also plugged a direct ethernet cable from the router to the Mac (I am using it now) and I've got no problem at all. So it MUST come from the WiFi Connection of the Mac.

Please let me know what I could try to do to make it better. This is getting at a point where I can't even browse anymore.

PS : Do you know If I will get charged if I bring it to the Apple Store?

Thanks very much

Although Macs and Windows machines use the same standards for WiFi, I've found that some tweaking to routers can be helpful to ensure a smoother experience.

In particular, I've found that enabling SSID broadcast, makes a world of difference with Macs. Additionally, if you are using WEP encryption (as opposed to the more useful and modern, WPA or WPA2) not only are you at a significant security risk, but the Mac doesn't seem to perform as well as with WPA. And finally, if you haven't upgraded the router's firmware recently (or ever), now would be the time to do so.