I'm only growing two indoors on a sunny windowsill, but I had the same trouble - planted them probably 2 and a half weeks ago, watered well and then left them. I noticed by Saturday the compost was really dry, but ignored it because no sign of growth. But to my relief, when I looked on Sunday, there was a tiny little shoot appearing above the compost, so I gave it a drop of water, though very little. As yours have only been planted a week, going on how mine performed, it could be another week or so before they start growing. Technically you should wait for signs of growth - bear in mind the usual method of starting them off is to sit them half in compost in trays till they start shooting, and then plant them, so they wouldn't be watered under those conditions. I'll be interested to see what others advise.

Iwould water them if they,re dry, but make sure you don,t get any water in the hollow stems.
they should start to produce shoots in 3-4 weeks, when the shoots are about 4" long you can start to take cuttings, cut just below a leaf joint, but make sure that there is another leaf joint below where you cut so that it can produce another shoot which you grow on.
I wouldn,t close all the blinds in the conservatory, just shade them a little, {it might speed things up a little if you could give them a little heat, especially overnight. }
good luck!!!
ps your cuttings will flower this year, and produce usable tubers.

pots sound rather large....are they field tubers, or ones you buy from shops....

good point, Scrumpy... I hadn't noticed the 12 inches mentioned - I started mine off in 4/5 inch pots.

thanks everyone. i've used 12" pots because thats what i read in an article on google and also someone on this site suggested a pot at least that size should be used. Maybe i've bought large tubers but there is no way i'd have got the majority of them in a 5" pot. Thanks for the tip about cuttings Derek. I've also sown some Dahlia's from seed which at the moment are doing really well, and they dont take up nearly as much room as the tubers. Still not sure whether to water or not, conflicting advice here, so i'll sleep on it. Thanks to you all though :0)

You'll be surprised at the lack of space needed to plant dahlia tubers and the small amount of compost needed.
Have a look at how you could set them out in my blog

http://www.growsonyou.com/scrumpygraham/blog/13412-the-dahlia-season

There are 9 field tubers in one of the trays.

Tilly, if the compost has shrunk away from the sides of the pot and is dry all the way through, then a drop of water won't hurt, but literally just a slight dampening rather than a proper water. Trouble is, in pots that size, it's hard to know whether the compost is as dry as it looks around the tuber itself.

yes i think i'll try that Bamboo. Will have a look at your blog Scrumpy, thanks for the tip.