Thanks for all of your replies
Well I phoned Sky last night and said I wanted to get Multi Room.
The girl said she would need to cancel my HD install and then get a new date - so they could do both together.
I said no way - I have been waiting for 2 months for my HD date
She then said to have the Multiroom installed at a later available date would incur a further charge
I said no thanks, and could she tell me the next available date.
After a long hold, she finally came back on and said she had put a "Same day resolution" note on my account. So when the engineer comes to fit HD he can then ring Sky to get a job number, and then fit the Multiroom.

With no extra charge.
Now why could she not have done that in the first place
Anyway, thanks for all of your advice, I am glad that I phoned Sky when I did, and finally managed to get a satisfactory resolution
Looking forward to some HD on my 60" Pioneer KRP-600A