5. Buy the best reasonable backup solution you can
No, you don't need the dual-drive robot, but you do need a solid, high-capacity tape drive and a bunch of tapes. SMBs tend to live or die based on the availability of data, and if you're operating with a small or non-existent IT department, these tapes can be the only thing between a functioning company and oblivion. I'd advocate disk-to-disk backups here, except that SMBs should be taking tapes to an offsite location (home) weekly, or even daily. If you're particularly diligent, buy a few 1TB external USB drives and run monthly backups to those, too.
6. Two servers: That's all
Naturally, this can vary with the size of the company, but if an organisation has fewer than 100 people and is using a modern hypervisor, two dual-CPU quad-core servers with enough RAM and storage will be all that's required to run the whole server infrastructure. If you add a physical server to handle backups, it can be an entry-level box that can run the tape drive.
7. You need firewalls and switches
You do need network switches and firewalls. As for firewalls, stay away from consumer-grade devices, but again, you don't need anything terribly expensive. You can get a decent SMB-class firewall with VPN tunnel termination for a few hundred dollars these days.
8. Desktops are cheap
A basic business desktop system with maybe a Core 2 Duo processor and 1GB or 2GB of RAM is probably more than sufficient for most users.
9. Operating systems aren't
Careful when buying that PC though. By default, it comes with Vista Home Edition. You'll need the Business Edition, which adds 25 percent to the price. Unfortunately, there's no much you can do about this, except...
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.