it's too late... everything thing we do is being recorded somewhere and for xx number of years... all these web browsers that claim they are more efficient of helping you search is all about digital footprint. Personal computers and laptops with a quick install can tell whoever which keys you press the most...
...in the USA any type of attempt to mask your ip immediately places you on the fbi ic3 watch list (like like those fools on the nigerian watchlist)... best thing to do is stay small and let it be...
Please don't listen to this. While it is true that federal regulation requires an ISP (Internet Service Provider) to provide a readily accessable location for law enforcement to monitor and record internet traffic this isn't something that's done remotely. I know this because I was an MP with the military for four year and am now a network engineer. This is kinda my field.
The truth is I always recommend a proxy whenever doing anything "questionable" on the internet. You can get plenty of information on setting up a proxy with a google search. <ahref="http://www.freeproxy.ru/en/free_proxy/howuse.html">How to set up a proxy</a> (I don't know if html code works on this fourm, if it doesn't then just copy the url and paste it in your browser.)
What a proxy does is sends all your traffic to a proxy server which then sends your packets to their original destination, the same route is followed back (not the exact route but it's easier if you just think of it that way.) So to the outside world your PC is communicating with the proxy server and nothing else. Use a proxy outside the U.S. the government can't exactly get a warrant for a sever in China.
So what about if they got your computer? What information could they find? Well let's clear that out too.
Everyone knows about clearing your browsing history. So I wont cover that. The part most people forget is the Domain Name Service or DNS. Always flush your dns when you clear your browser. It's easy to do, if your on windows just open your command console by going to start and typing cmd in the run bar and press enter.
Then type "ipconfig /flushdns" without the quotes.
There are also some registry keys you could delete but honestly they're not going to do much to help with a conviction. As long as your proxy is up, your dns is flushed, and your cookies are cleared your basically good to go.
If you really really want to be stealth you can look into 10.ing (ten dotting) your ip address which is the best way to be invisible online but it's a bit more advanced than a simple dns flush.