arc4ne; whow, u forgot to mention whether u have other hdd? as for accomplishing dual boot, advise leave w where it is install linux behind it.
reduce w size (depending) on size of hdd. linux requires swapspace, one other thing how much memory installed? linux memory hog it needs more the better it is efficient. linux does have to be partitioned for each would become a (folder) w terms. please read this carefully;
http://tldp.org/HOWTO/HOWTO-INDEX section 4.1.8 Partitions and Filesystems expand for more detailed info. imperative!