Try and find a deal first – have a look at Digital Spy and AV Forumsto sniff out a free deal.
If you can't get one, call Sky and ask to cancel. They give free stuff to new customers but really stiff existing ones. Don't bother talking to a regular drone but the people in cancellations are paid to "turn round" customers and have the power to give you free stuff. Mention you're thinking of going to Virgin if the going gets tough. You should get a free box and free installation. If you don't – hang up and try again. A different operator will give different results.
Doing it yourself means a new twin/quad LNB, new cable and Sky+ box. May be difficult/expensive esp if your dish is hard to reach.
If you don't need/want HD don't get it. If you have a big HD TV and can afford the extra £10 then do.
BTW johntawn – HDMI cables carry 1s and 0s. It's a digital signal so it either gets through or it doesn't. The free Sky one is cheap and nasty and poorly made but it still works. Tested one back to back with a £90 QED cable on a 1080P projector with a 100" screen. NO DIFFERENCE.
Better shielded cables are worthwhile over longer distances to prevent drop off and better constructed ones are more resistant to constant handling but that's it. Save your money for some Blu Rays 🙂