Interesting article. They use old hardware, but here's how you can do it:
1. Get yourself a motherboard with at least half as many PCIe slots as you need monitors. Since there are PCIe x1 graphics cards (HIS makes a Radeon x1300 for PCIe x1) out, you can count those too. Your best bet would be to get a motherboard based on the NVIDIA NForce SLi chipset or ATi CrossFire. The Intel 975X will also work in this case too. That gives you two PCIe x16 slots and at least two x1 or x4 slots as well.
For this example, let's assume that you a motherboard with 3 PCIe x1 slots and 2 PCIe x16 slots. (This is a common setup.) You are running six seats and want digital LCDs.
2. Since the GPUs need to be the same type and we need to use PCie x1 slots in this example, this means we'll be using ATi Radeon x1000-series cards. (HIS Hightech makes a PCIe x1 Radeon x1300- the only somewhat reasonably priced PCIe x1 card out there and one of two PCIe x1 cards out there period!) Get two HIS PCIe x1 Radeon x1300s and two PCIe x16 Radeon x1300s that have two DVI ports each on them. This will be four GPUs in total and cost you about $300-450.
3. Buy six DVI-input LCDs.
4. Buy six sets of USB mice and keyboards.
5. Make sure that your power supply is stout enough. The Radeon x1300s are not very power-hungry but will still probably consume up to 150W as there are four of them. I suggest that the PSU be 500W or better.
6. Install the latest AMD/ATi Linux proprietary driver for the graphics cards.
7. Have Xorg use each attached screen as a separate X server, including the two screens connected to the two dual-DVI cards. Note that while the mouse and keyboards go from 0-5, the two monitors attached to the dual-DVI cards will have a different "Monitor" and "Screen" setting but use the same BusID as they're attached to the same card. The two PCIe x1 cards only have one DVi connector, so they'll have unique BusIDs.
8. Continue to follow the Linux Gazette guide.
You should have your multi-head, multi-session setup right there. I might take some flak for using ATi hardware and it's a tiny bit tougher to use one card for two monitors, but it's what would work in this case and it does work in this way (my dual-DVI x1900GT can do this as well with its two attached monitors. Usually I have it in spanned-desktop "conventional" dual-head mode.) This would be a more modern and less costly approach to the setup mentioned in the Linux Gazette article.
I'm not a big Windows Fan in the first place, but I want to play games while my wife does her homework, so I'm kinda limited. lol. You'd think Windows 64 or Vista would have this implemented by now. You can get way too many cores in a small box these days, need to be able to use them, lol.