Hi Ian, agree with above - I found the software is rarely the issue. If you don't have another computer to test the connection on do you have anything else that's WiFi (assuming you're using WiFi that is) - iPod, PS3 etc or, on that machine do you have anything else that uses the internet that you can test eg iTunes... or do both. Another device will prove the connection, another app the browser.
Run a full system scan - make sure there's nothing lurking on there that you don't want!
Also, have a look down by the clock for any icons that might indicate something else is happening - if any apps are downloading web updates you should see a notification there - that can really hamper connection speeds - especially if they're downloading a major upgrade.
Finally, if you are running a wireless router that may be the issue - while convenient WiFi really is hit and miss (rubbish IMO). If you have one connect the computer to the router using a network cable - I got this a lot! If the two are close enough bin WiFi! I know with Netgear (from experience) the routers can "wear" over time, hard to diagnose without another though. Try rebooting the router (switch it off and on again) - 2 things, sometimes restarting the services will put things back on track and secondly, if you have someone leaching your service it will kick them off! For a while at least, if it's a pre pack from the ISP it should be secure.
This all assumes of course that you have rebooted the PC first! Also, make sure you're hard drive is not too full - it will hamper writing paging files (virtual memory).
Good luck!