Thanks for all the replies, everyone. I spent far too many hours last night playing with this, and still have not managed to get it to work...
MiniMax - I have tried using SCUMMVM: it works fine with a demo of the game, but cannot recognise the files from the floppy disks as a game, presumably until they've been installed. I have done a search of the SCUMMVM forums and they seem to advocate using DOSBox to install the game!
I have also tried installing the disks without DOSBox, but it comes up with a DOS-like background that says much the same thing and disappears very quickly.
Something weird I have noticed is that there are two install files, both batch files, one called "install" and the other "_install". If I run the second of these without using DOSBox, it asks me to insert disk 2, which I do, then it asks me for the disk with the batch file. I put disk 1 back in again, which it then tells me is not formatted.
However, if I run the "_install" file from within DOSBox, the same thing happens up to when I insert disk two, where I get a dialog box saying the wrong volume is in the drive, please use 'MONKEY 1 XL'. I insert disk 1 again and click 'try again', and it hums and clicks for some time, before telling me that the installation was unsuccessful, and it may be because my hard disk is full, as it needs (all of!) 4.8mb. I have tried limiting the space of the C drive using the freespace command to 5, 8, 10 and 50 mb but the error still comes up.
collector - I'm sorry, I don't quite understand: what is a disk label?
cmw - "install c:" is what it says to do in the original manual. However I've tried simply putting "install" and "_install" (see above), and it makes no difference.
Sorry for the long post - just wanted to show you all what I've tried.