mplatsdk.exe is the binary redist name for the CE 2.00 SDK.
There is no SDK for CE1 as you would understand it from later releases.
In order to formally code for CE1 you need Visual Basic / Visual C++ 5.0 and the Windows CE Toolkits for Visual C++ / Visual Basic 5. There are existing threads on this.
There are also known methods of forcing the 2.00 SDK compiler to build for 1.0x:
http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=4062&pos...
http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=4110&sta...