Jmmijo's comment relating to chip ram is on target. Each connected disk drive required some chip ram to be used for buffers, and on a 512K chip ram Amiga, some software needed as much chip ram as possible in order for it to run. To simulate disconnecting all external drives in WinUAE, go to the "Disk Drives" page in the GUI, and select "Disabled" in the drop-down lists for DF1:, DF2: and DF3:. When you start the emulation, the emulated machine then only "sees" DF0: so if that is the only issue everything ought to work.
As for what WinUAE stands for, the original version of the emulator was UAE, which stands for Unix Amiga Emulator (it was targeted at Unix machines). When the Windows port was started, the "Win" prefix was added for some unfathomable reason.
