RunDLL32.exe

Run a DLL program. This command is available on all version of Windows from Win95 onwards, but the DLL's and options available do vary considerably. Many options are case sensitive.

Syntax
       RUNDLL32.EXE dll_name,EntryPoint [options]

Examples

Un-install MS Java Virtual Machine (JVM):
RUNDLL32 advpack.dll,LaunchINFSection java.inf,UnInstall

Copy a floppy disk:
RUNDLL32 diskcopy,DiskCopyRunDll

Lock workstation:
RUNDLL32.exe user32.dll, LockWorkStation

Add a Network Printer:
RUNDLL32 printui.dll,PrintUIEntry /ia /c\\server /m "AGFA-AccuSet v52.3"
/h "Intel" /v "Windows 2000" /f %windir%\inf\ntprint.inf

Add a Local Printer

RUNDLL32 printui.dll,PrintUIEntry /if /b "Test Printer" /c\\SERVER
/f "%windir%\inf\ntprint.inf" /r "lpt1:" /m "AGFA-AccuSet v52.3"

Add a printer connection that's available to anyone who logs on:
Rundll32 printui.dll,PrintUIEntry /ga /n\\Server\PrintShare

Display all the available commands for PRINTUI.DLL - add/remove print drivers, print queues, preferences, properties etc:
RUNDLL32 printui.dll,PrintUIEntry /?

Note that PrintUIEntry in the above examples is Case Sentitive.

“If you're rich you can buy books. If you're poor, you need a library” ~ John Kenneth Galbraith

Related:

CON2PRT - Connect or disconnect a Printer
Qchange.vbs - Change Printer Connection
PRNCNFG - Add, delete, or list printers / connections, set the default printer.
PRNMNGR - Add, delete, or list printers / connections, set the default printer.
REGSVR32 - Register or unregister a DLL
WMIC PRINTER - Set printing options through WMI.
Bruce Sanderson - Setup shared printers (PrintUI.dll)
DX21.com - A long list of rundll32 options
Q189105 - Add Printers with No User Interaction (Win 2000)
Q314486 - Add Printers with No User Interaction (Win XP)