Migrating a hard drive from Windows to Unix can be done, depending on some of the variables in play with the particular system in question (for example hard-drive make/model/type and same for hard-drive controller) it can either be done fairly quickly, simply and painlessly......... or not. For this reason it will help to do a little planning to improve the chances of not getting sucked into some of the potential boobytraps.
Below is a link to a site you may be familiar with, specifically addressing your question. If nothing else, it may help prepare you to at least gloss over this info, at least parts 1 and 2, before digging in.