Financing Computers for Business?

Mercutio asks: "OK, I've been handed the responsibility of acting like a grown-up and changing from my normal day-to-day IT job to actually making decisions involving someone else's money. Specifically, I've been asked to deal with all the variables associated with purchasing/leasing computer equipment (desktops, laptops, printers etc) and I'm feeling a bit out of my league. Anyone have any tips for dealing with leasing or financing equipment, companies to avoid working with, or mistakes made in past leasing/purchasing arrangements? Any company that was really great to work with? Any help is of course appreciated. Thanks."