Yes, now. What you'll aim to do is get the tubers into growth, and then, with a clean, sharp knife, cut them so that each cut portion has a nice strong shoot on it. Pot each into good potting compost (multi-purpose) and put somewhere frost free, but not too warm, to grow on. A cold frame with ready protection is good. I'm going to admit here that I've done it a few times, but now prefer to use someone else's labour and buy new plants! W

thanks Worthy,its best i put the effort in, as its for the mother in law [keep on her good side?]

You can do both. Cuttings is the best way, as when you take them fresh growth appears from the spot you've taken the cutting from. Then, later on, you can divide the tuber should you wish.
You will get better plants from cuttings.

Just remember that the tubers themselves have no growth points. the new growth comes from the stem and the tubers only act as food stores.

Not quite correct. A dahlia tuber is a collection of individual tubers, each tuber being attached to the stem. So yes, it is the food source, but is also the growth point.
In an ideal world there would be 4 or 5 "chicken legs" as they are called, all branching nicely around the stem. The "eyes" form where the leg joins the stem, so to divide them you cut this leg and eye away from the stem, with a bit of stem attached. I'll put a picture of one on later.
I say ideal world, that never happens. You can have a tuber the size of a football, but there may be only one suitable eye on it, and you can never always tell where it is until they grow.

http://www.growsonyou.com/photo/slideshow/264770-chicken-leg/member/scrumpygraham

http://www.growsonyou.com/photo/slideshow/264771-chicken-leg-2/member/scrumpygraham

http://www.growsonyou.com/photo/slideshow/264772-tuber/member/scrumpygraham

1st picture shows a chicken leg
2nd Picture shows where to cut the chicken leg
3rd picture is a tuber without legs, just a large crown and stem. To divide that one, cut straight down the middle of the stem

thanks Owdboggy and Scrumpyg, very informative. The tuber is almost the size of a football, so i think i will attempt both options
cheers again kev