And now for the actual thread.
RUNDLL32.EXE, according to Microsoft, has the purpose of running a DLL as an app, that is, running a routine inside the DLL standalone. The reason for there being two instances of RUNDLL32 is simply that two DLLs are running, and they probably have nothing to do with each other.
The problem is just that you don't see which DLLs are running, only RUNDLL32 itself. But there's nothing inherently wrong with there being multiple instances of it.
Try running "msinfo," or Microsoft System Information. You can review much more extensive listings of all currently running processes, tasks, handlers etc. there.
It also helps to look at WIN.INI, all Registry keys starting with "Run" (RunServices, RunOnce, etc.), all items in the "Startup" folder in both your personal Start menu and the one for all users (C:\WINDOWS\All Users\...) to see what all is launched at startup. If you see anything in the form of "rundll32.exe <something>.dll,<something else>" you can probably tell by the DLL's name what it is.