Macbook Pro Wifi Issues- Connected, but browser won't work for up to 5 minutes

I have had my Macbook Pro since Mid-late 2009. Running current Lion version. I always use WIFI networks, never had an issue. About 2 weeks ago, when I connect to ANY wifi network, the computer connects, I go to Safari or Firefox, and the page will load for 3-5 minutes before the internet works just fine. If I stop using the computer, or am reading a page for 10 or so minutes, it will do it all over again. What is really strange is that I also run VMWare for work, and if I go right to the VM Ware Windows side, the internet works immediately every time- no delay. Why is the WIFI working on the Windows side right away, but taking 5 minutes to work on the Mac side?

Anyone that can help me would do me a huge favor!

Also- I have iPhone 4s, iPad 2 and 1 and they all work right away on all the same networks.

Thanks,

Mark