Getting no response here, I contacted Mindomo. This is their (5 minutes ago) response –
Hello Rob,
and thank you for reaching out to us. Indeed, Mindomo Desktop doesn’t support Windows XP as this is currently a rather out-of-date, unsupported operating system.
Please don’t hesitate to contact us if you have any further questions.
Best regards,
Sergiu Paraoan
http://www.mindomo.com
Phone: +40 (0)256 486 430