Combine half the sugar and all of the water in a heavy medium saucepan.  Scrape the seeds from the vanilla bean into the pot along with the pod.  Bring to a boil, lower to a simmer and cook for 5 minutes.

Add remaining sugar and stir to dissolve.

Add rhubarb.  Bring to a boil, reduce heat, covered and simmer until rhubarb is just tender, about 8 minutes.

Add strawberries and bring to a simmer.  Cool.  Cover and refrigerate until chilled.  Can be prepared several days ahead.  Remove vanilla pod before serving.