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First off, If you want to keep windows or be able to install it (M$win)
make sure you keep the recovery partition intact,
If you only have the one OS (M$win) installed at present, on one harddrive partition
you will need to defrag win first.
Check out how much free space you have,
using your favourite GNU/Linux distribution dvd/cd-rom create new partitions in the free space.
You'll need a (arguably) swap, root and home partitions.
Make home the biggest, swap may be about the size of physical ram or more (up to 2 gig).
hope this helps, Glenn