This cannot be stressed enough. As Joel Spolsky notes (based on Steve McConnell) in item No. 9 of the Joel Test, you need to "use the best tools that money can buy".
If you buy old, broken and/or barely functioning hardware, you'll spend a lot of time debugging the problems there, which will waste a lot of precious time. And you may lose a lot of reputation and customers due to down-time. Relying on reliable, high-end hardware is a much better idea.
I've been to two workplaces that gave me an old computer with a 40 GB hard-disk. It wasn't enough at all. At one place, we've reached the limit of this hard-disk due to several large source code checkouts, and as a result needed a bigger hard-disk. And the only hard-disks the lab had were 80 GB ones, which were bought because they were the cheapest (per-disk, not per-capacity). Please, buy large enough hard-disks.
At the same workplace, I was given a computer with a read-only CD-ROM drive. It was not even a DVD reader. I brought a DVD of audio files from home, and could not read it. In this day and age, read/write DVD drives are the standard, and are ultra-cheap.
Sometimes you'll need several computers, or a decent virtual machine emulator, to run alternative operating systems on the same machine.
Make sure your workers have a high-quality screen. They need to look at it most of the day, and they want it to look nice. A decent 19" LCD screen nowadays is very cheap, and well worth the added productivity.
You also need a state-of-the-art version control system , of which there are currently several high-quality open-source alternatives. Some very costly version control systems have a bad reputation for being extreme troublemakers, while the modern open-source alternatives "just work".
If there's a good commercial software that your employees like to use and can recommend, don't hesitate to buy it. You'll also find O'Reilly Safari Licences to be a good idea so your employees can easily look up and read information in many books online.