Well, it's the end of a whole day of tearing my hair out, but I finally calibrated my printer (an Epson R2400). Yipee. The problem was that ColorSync on my Mac was interfering with the setting of the profile. I finally found a way of getting around it through a video on YouTube at this address: http://www.youtube.com/watch?v=0tw9qPRLuNw
I have to say that the service from X-rite was atrocious. They didn't answer any of my calls, and sent totally unhelpful emails in response to my queries. I wouldn't recommend the color munki for that reason.
The next question is, what should I do tomorrow? Should I hire a cable detector for £20+VAT which may not work and try and locate cables, or should I wait and see if my Dad who's coming on Monday can work it out. I reckon I'll do that. It's worth a go. Looks like tomorrow may be a day for having a cup of tea with my friend!