This article is from the Macintosh for sale FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
The short answer to this option is DON'T. If you're VERY
strapped for capital think about it, but most commonly the lease
payments over the term of the lease add up to as much as or even
more than the cost of the system itself plus the interest on a loan
to buy it. If you absolutely must lease try to keep the term as
short as possible. Generally Mac power doubles every year while
price comes down by about a third. You don't want to lock yourself
into obsolete equipment. The most common lease term is two years,
but with a little shopping around you can find one year leases.