Geeez!
I can't believe the amount of mis-information on this board!
O.K. from Canada here's some info:
First off, never mind your hard drive, if your on the internet, CARNIVORE (or similar programs) are what the DEA tracks your email and surfing with often enough. These are at you ISP anyway so they can track your email without your computer hard drive anyway. THAT'S how they got that guys emails!! Never mind the hidden .dat files and history files on your computer and all that other kiddie stuff.
Also as for wiping your hard drive, the only sure way is to get one of the LEO's programs themselves. In Canada the RCMP has a program that totally wipes hard drives. They use it when they dispose of thier OWN computers. A fellow in my office (a non-enforcement govt. department) borrowed the program to erase (really erase) his hard drive before surplusing it. The officer he got it from told him that it definately worked cause the RCMP couldn't even recover data after it was used (that's why they use it themselves). However, it is also a criminal offense to have possession of this program anyway (or so he was told). He had to return the program after use (on an "uncopyable"CD).
Unless your surfing through multiple proxy, the DEA can track your websites anyway (and they do from your ISP anyway) let alone your email. If your surfing
www.sellingbaddrugs.com likely they will start monitoring your email after a few visits. Ahhh the wonders of a "free country"! Hello Mr. Orwell!
Want to find out alot of the "real" stuff? Hang around the pot-grower's forums (some are good, some suck). They have ALOT more to loose than guys selling steriods. They are treated much more harshly too by the courts. These guys are indeed on top of things as far as computers go and are quite willing to give out what they do know.
My 2cents.