OOOh a long time since I've been able to do the full splits.
If your body was there once then it should be easier to get back to it. I did ballet and other dance and gymnastics and am still very flexible but not having done that kind of work and now having arthritis has put paid to being quite that flexible :)
Some tips here...
http://www.bbc.co.uk/blast/dance/advice/tips/d oing_the_splits.shtml
Take it easy though, if you've not been that flexible for a while then don't risk overdoing things and causing yourself an injury by pushing it.
Yoga and pilates should help with general flexibility and they should teach you how to go through levels and extentions at a reasonable pace to get body ready.