For ZX81 emulation, set CPC$ZX to 81. It should work both in multitasking and singletasking modes, but I wouldn't try
switching (so if you want singletasking mode, use CPC$Wimp 0). This has very many rough edges. In particular, there's some
support for ZX81 hires (an amazing 256x192 in 2 colours!), but this is not perfect. If you're unlucky the emulator may crash. If
you're very unlucky, this may take down the whole machine. If you're extremely unlucky, it could conceivably wipe your HD
as well. Well, you've been warned. Even if you're not using hires, sometimes the screen may go into vibromode -- this is
especially easy to do with FAST mode. Sorry. 

ZX81 files should be placed in a directory pointed to by ZXTape$Path (don't forget the trailing dot!). These should be in .P
format. You load, well, by pressing J (LOAD) then Shift-P (") then the filename, then Shift-P again. If it all goes OK, fine. If
not, you'll get an error Z/0, in true ZX81 style. You can save, too. 

The main source of ZX81 stuff is ftp://ftp.nvg.unit.no/pub/sinclair/zx81, though there are a few WWW sites around. If you've
forgotten what the ZX81 keyboard looks like (how could you?), here it is. To make your life a bit easier, note that Ctrl will do
Function (i.e. Shift-NewLine -- remember to release it before pressing the next key though), Tab will do Graphics (i.e.
Shift-9), Delete will do Rubout (i.e. Shift-0) and Esc will do Break (i.e. Space). The arrow keys will do cursor movement (i.e.
Shift-5/6/7/8). 

I've risked including a ZX81 ROM image with the release. It isn't clear who has the rights to the ZX81 ROM. If it's Amstrad,
then I have their kind permission -- many thanks, Amstrad. If it's Sir Clive, then I don't. Er, please, Sir, I meant no harm,
please forgive me, grovel, grovel...