If you're in the US, I don't think it's recommended to throw it in the trash. Every county in my state has a "consumer electronics recycling day" where you can take said items to a central location for proper disposal. Mine's coming up and I have a stack of old computers and things to go out.

Apparently, many elements in computers contain lead, mercury, and other nasty things. If you're in the US, look for electronics recycling in your area. Start on your state's web page (http://www.state.nj.us/ for example), drill down to the recycling section, and look for electronics.

<rant-ish>
After recently reading about how mercury leached into the environment has poluted the bodies of large populations of shark, trout, and other sea life; I'm very concerned about putting this stuff back into the environment. Sure, mercury probably gets to the fish because manufacturers are dumping into oceans, whos poluted water is harming the small fish living in it, which polutes the bodies of larger fish that eat them.

So the polution is probably not from landfills, but consider this: If we continued to use old computers, we wouldn't need new ones, which would lead to less manufacturing, and thus less polution. And why do we need new computers? Because Microsoft and the lot continues to give us unnecessary "great new features that we need" thus antiquating our hardware, causing tons of perfectly working parts to go into big holes in the ground for no reason.
</rant-ish>

Hey, if you don't need those 4gig hard drives, hook me up! With a smart install of Win2k, the average business user (using computers that I manage) hardly fills a 4 gig drive. Seems easier to use old 4gig or 8 gig drives than buy these 40gig monsters that they never need. I've always always wondered if computer hardware makers could use modern technology to make previous-generation-sized parts, could there be a reduction in size, materials used, and thus cost? (ie: use current HDD density and speed to create 8 gig drives. they'd only need one platter which could probably be half the size, thus needing a smaller metal enclosure (brought up to 3.5" size by plastic spacers); all of which should cost less, right? same for laptop processors. 90nm technology for a 1ghz machine = smaller, cooler, simpler, less power hungry, less heat, less cooling = less cost)