I created a partition with GParted and ran the installer. In the initial screen, all the icons at the bottom lit up.
The first time I tried to format the partition, which had been pre-formatted as ext, Haiku gave the error "Drive setup could not be launched."
I then deleted and recreated the partition, taking care to leave it unformatted, to see if that helped. On that occasion, there was no error message: clicking on the desired partition had no effect.