Go to, http://speedtest.net/. About in the middle of the page on the left side is your IP address, copy and paste than into your address bar to access your router.
If you haven't fiddled before the name and password should be the defualts (which outta be documented somewhere) but with some fiddling you can add wireless security like WEP/WPA. My router is literally 1 click to get to security settings, choose one, set a passphrase and apply. It may or may not be that simple for your current router, but I'm sure it's possible and you can likely find online manuals from the manufacturer by googling the model number.
DO NOT however start messing with anything you don't understand...
Also try calling your ISP up and seeing if it's something on their end. I've had slow speeds before because of something on Verizons end and we had to call them to get them to fix it. Although I think they claimed not to see a problem at first, but found it shortly after during the same call.
Just remember if you add security you'll have to change the settings on you Laptop and PS3 to reflect those changes.