Q: How can I safely dispose of an old MAC Tower?

While a bit of a political statement, "safely dispose" and "electronics" often don't go together in the same sentence.  Even local recyclers can (not all, not always) end up shipping off e-waste to distant lands with less-than-stellar pollution histories.  Give it a bit of research if it interests/concerns you.

One way to get a machine off your books an on to someone's who might apprecitate it more might be through the likes of ebay, your local craigslist, Low End Mac swap, and so on.  That also has a better chance of extending the useful life of the machine itself.

If by "safely" you really mean "securely," you can simply recycle or sell the machine without the hard drive.  Or wipe it with Disk Utility.

We assume that you are not in a state like Washington that has an e-cycle program.  Our city also has an incinerator that burns and scrubs the smoke to minimize polutants.

The only part of the computer that is 'hazardous' is the pc boards.  In bulk, you can sell them for $4 a pound so there is even a market for the boards.  It is the labor cost of disassembly that makes recycling difficult.

Finding a new happy home is the best but they will want the hard drive so wipe the drive enough times to satisfy your privacy concerns.  No easy answers but plenty of options.

BTW, what version of tower?  Our youth group would love to recycle an X Server.

Glad we could be of help.  Keeping a machine in appreciative hands is a great means of "disposal!"