Having found that OO only works with a 32-bit JRE I've installed it, but OO says that neither C:\Program Files (x86)\Java\jre7 nor C:\Program Files (x86)\Java\jre7\bin contain a valid JRE. But as far as I can see they're OK, and going to the bin directory in a console session and doing a "java -version" certainly shows a 32-bit JRE.
Here we go again! Has no one ever heard of a Forum search?
The authors of Java 7 changed some of the entry points, with the result that some Java 6 applications fail. One of these happens to be OpenOffice. Under Windows one must install a 32 bit Java (because OpenOffice is a 32 bit application) and because of the changes in Java 7, this must be Java 6. A 32 bit Java 6 can be downloaded from the second link in this posting http://user.services.openoffice.org/en/forum/viewtopic.php?f=15&t=54746#p240389
Apache OpenOffice 4.0 on Xubuntu 13.10 and Win2K/XP