There's a suprising amount of accuracy in Pipe's post despite it being a Pipe post.
...I'm kidding Pipe. I love you. I want you inside me.
But regardless, yes, the tendancy for THC to linger in your system is entirely related to your fat content, since THC "sticks" to fat cells. There's a couple ways you can flush out the THC. First, is naturally, by drinking a lot of water, or cranberry juice. But be wary that cranberry juice will wreak havoc on your ass; it's a natural laxative (hence it's detoxifying properties). Another way is good old fasioned exercise, but be absolutely sure you dont exercise anywhere from about 3 days until the drug test to the day of. The THC will 'dump' into your system and THC in your urine will spike.
As far as hair samples go, you're ****ed. Any sort of THC will cling to hair like a Cuban to his raft (haHA!). The best you can do there is Lice treatment or lots and lots of head and shoulders. Also hairspray/gel to mask the THC.
It should also be noted that drinking a ton of water looks very suspicious when they're testing your urine, because they can detect diluting a sample. I've cleared drug tests in less than a week by simply drinking about a gallon of water a day (a little less than my max, but I work out, so yours might be a bit lower.
And if you do use someone elses' urine, strap it in-between your nuts and nutsack, and wear it there for a awhile before the test. You need to bring that sucker up to body temperature, because they test for heat as well. Pipe mentioned chemicals that bring it up to temperature, but it should be noted that they can, and will, test for that (even my ghetto-ass 'let's get this **** over with you ****ing stoner' place tested for it).
Hope that solved all of your questions! As for viracity of all this, I'm a proud supporter of TCCwiki: helping druggies since 2005!
--Harrm