UMBPCI is a hardware-UMB-driver for DOS and Win95/98. Windows ME ignores the CONFIG.SYS, so there is no chance to load UMBPCI.SYS except you reactivate the CONFIG.SYS with a patch.
UMBPCI is a hardware specific UMB driver with some limitations and problems, so don't use it without a good reason, especially not on boot disk which shall work on many different computers.
UMBPCI extends the HIMEM.SYS of DOS or Win95/98 by the function 'Request XMS UMB' (These are the 160 Bytes which stay in memory). That's the same thing that EMM386 does, if you load it with the parameter 'noems' or 'ram'.
UMBPCI makes UMBs from disabled memory that is intended as Shadow-RAM. UMBPCI enables this memory and disables its write protection.
It needs only 160 Bytes of low memory, that's all!