10. Wait for Windows 7
There's no sense in buying anything with Vista right now. Wait for Windows 7 to become a pre-installed option and go from there. October 22 is the official release date.
11. Don't get a T1
Unless there's absolutely no other option, don't bother with a T1. Business-class cable or DSL will suffice, and they offer much more bandwidth for a much cheaper monthly cost.
12. Host your Web site somewhere else
Don't even think about trying to host your Web site at your location. Your Web presence needs to operate even when you don't, so pay the few dollars a month to a reputable hosting provider and let them handle the redundant bandwidth, power, and server needs.
13. Don't confuse users with employees
Unless an employee is spending the majority of their day in front of a computer, they're not a user -- they're an employee. When sizing hardware and software, calculate your requirements based on the number of people that will actually be served, not the number on the payroll.
14. Hire a competent consulting firm
Don't hire Bob the Computer Guy to set this stuff up. Find a consulting firm that typically works with larger companies. If there's no full-time IT person, all this gear will need to run without much supervision for as long as possible -- and that can happen only if it's set up right the first time. You'll probably be charged more per hour, but the returns will generally be worth it.
Naturally, every business has nooks and crannies that the above rules can't fill, but by and large, a business in a single location with fewer than 100 users can get by just fine with these simple rules. There's a fine line between being cost-conscious and putting your business at risk with shoddy hardware and software, but dealing with those issues is part and parcel of operating a small business. Some parts of IT can stretch pretty far without breaking, while others are not to be trifled with. Knowing which you're dealing with is the key to doing it right.