Hi
Following link has info about date validation that can be created in InfoPath, Hope you find it useful!
http://groups.google.co.in/group/microsoft.public.infopath/browse_thread/thread/ba5d71832db4815a/4c6ca45a7317edda?lnk=st&q=day+validation+in+infopath&rnum=9&hl=en#4c6ca45a7317edda
Madhuri
http://www.ggktech.com