Upgrade from Sky to Sky+ . Do I need to go through SKY for this?

Hi there, I have SKY multi-room. The sittingroom has the Sky+ box and the kids TV room has the "normal" Sky box. The kids are coming in the whole time to use the SKY+ box look at programmes they've recorded. My wife and I are getting a bit tired of this, so we've decided to get a Sky+ box in their TV room. I called Sky to place an order for this. They took my order and said it'd be ready in 2 to 4 weeks. True enough, I got a mail after nearly 4 weeks telling me my order was ready to be completed.

I called the number they gave on the mail and I paid €295 (€195 for sky+ box and €100 installation; they tried to push the HD box on me, but as I don't have a HD TV there's no point in me going for this ... plus I don't want to pay and extra €14.95 per month for this).

They were able to process my payment but weren't able to give me an installation date due to technical difficulties with their system. The guy I spoke to said that he had taken a few booking earlier that day for people in Dublin and there were still some slots available for installation on Saturday. As he wasn't able to give me an installation date, he gave me a number to call but said that the team who arrange installations were gone for the evening and suggested I call them the following day, which I did. When I got through, the earliest date they could give me was July 25th (over 6 weeks away).

My question is: Do I have to go through SKY for this upgrade or are there other installation companies that I can use?

Thanks!
Gerry