24 volts down to 5 volts at 5 amps. OK, if you really want to use a huge
heatsink! Thats 95 watts of heat.

If that still appeals to you look at the National Semiconductor app notes
for the 7805 or LM340 regulators. You'll see a current boosted circuit
using a 78xx, a big(or in your case, a few paralleled)PNP power
transistor, and a low value resistor. It is not ultra hip, but very easy.

After you see how much heat 95 watts really is then look at the one-chip
switchers. National also makes a 5 amp version of those. Not the most
efficient, but very easy to use.

Cheers,
Bob