Here's the AppleScript code to facilitate launching it multiple times:
property RDPathMac : ""
on run
if RDPathMac is "" then
tell application "Remote Desktop Connection"
activate
set RDPathMac to (path to application "Remote Desktop Connection" as text)
quit
end tell
end if
tell application "Finder"
if not (exists RDPathMac as alias) then
tell application "Remote Desktop Connection"
activate
set RDPathMac to (path to application "Remote Desktop Connection" as text)
quit
end tell
end if
end tell
set RDPath to (POSIX path of RDPathMac) & "Contents/MacOS/Remote Desktop Connection"
do shell script quoted form of RDPath & " &> /dev/null &"
quit
end runCopy this text into Script Editor and save it as an applet or bundle, then drop this puppy in your Dock or just a convenient place to double click it, and laugh your way to multiple Windows connections!
More specifically, this script nicely checks to see if you've used it before, and if not, it runs Remote Desktop twice -- once to establish the path to the app, and once to actually open a new connection window. Every time you run the script after that, it will simply launch a new Remote Desktop Connection process.
[robg adds: gabester also provided this zipped archive that includes the compiled script along with a custom multiple-RDC-apps icon (note that I haven't tested this script yet). This hint explained how to run multiple copies of the prior version: you basically duplicated the app as often as needed.]

