Yes, that article says concurrent, that hack is made to have 2 people login at once.
since windows xp and non server versions of windows only allow 1 remote desktop connection at once, that hack allows for 2 concurrent users to login at once.

Windows servers have things called "sessions" windows server 2003 standard comes with 2 sessions, meaning you can login as the same user up to 2 times at one time, OR have 2 users logged in RDC at the same time. Enterprise allows 3.
There is no way to "hack" and get more, b/c you NEED a license.

Although there are alternatives, like sahil3x1 said, you can use teamviewer. You can make multiple accounts and put teamviewer on each account and people can connect (but there ARE some flaws to that) i believe if the user is logged off you cannot login.

Your next best thing would be installing a VNC Server on the server itself.
Then users can login via a port for each user ( ithink you can set it up that way) and even if the user is logged off, they can login.


Alternatively, depending on the specs of the server and features (such as more IP's, although you do not need it if you use VNC) you can install VMWare and set up Virtual Machines (VPS's) and give them each their own IP, AND OR VNC Port.

But be careful with allowing many people to the same computer! They can do some harm, and it would be the owners fault!

best of luck to you , hope this helps