The guide specifies that 8.8 GB of free space is required. I removed some files to bring my free space up to 9.16 GB, but when I run the install, I come across this:
"A total of 11437 megabytes (MB) of free disk space is required."
The amount of free space required therefore appears to be about 11.17 GB.
(Incidentally, this is information that ought to be included in any guides to first installing Windows. I partitioned my drive for the installation and would have allowed for this free space had I known I might need it.)
On with my repair install now...
Update: I got my free space up to 11.8 GB, ran the install, and this time I got:
"There is not enough free space on partition (C

. A total of 16827 megabytes (MB) of free disk space is required."
16.43 GB now?! I'm not sure if I can get that extra 5 GB. Why is this figure changing?