I think the reply is incorrect as you CAN have several computers connected to a remote computer via RDP.
The Remote computer has to be a SERVER which allows multiple CONCURRENT logons --something like W2K3 Server is fine for this purpose --or if your remote machine is a LINUX server then use Tight VNC or similar.
Remember all you are doing via RDP is just logging on to the remote computer like you would do if it was in front of you at a local desk.
If it's a single user system like Windows XP PRO or W7 then only ONE user can log on at a time.
RDP doesn't affect this at all.
Note that your SERVER might need to be licensed if more than I think 4 concurrent conncections are active with W2K3 server. That's totally another story however. You can certainly have 2 concurrent connections with NO problems.