usually the fastest way to find questions is using google or the search option here on lq.
9 out of 10 times your question has already been answered
what you want is a called a "dual boot" and is a verry common thing to do, most people here have it.
when i search google for "dual boot mandriva" i get the following search result
http://www.google.nl/search?q=dual+b...en-US:official
this should answer all the mandriva specific questions.
good luck