A good setup would be to create three partitions totalling 40 GBs. The swap
aprtition would equal (but not exceed) double your RAM up to a max of 3 - 4
GB, root partition would be about 15 GBs, the home partion would be the
remainder. The mount point for root is / and for home it is /home. The
format could be ext3 or 4 with 4 being better but 3 being more compatible
with other OSes being able to read them. You won't likely fill up the 15 GBs
of root but if you do it can cause problems. If you are ripping a DVD or
accessing lots of multimedia the tmp directory can fill up quicker than you
would want. Basically Linux does not need defragmentation, but if you fill
partitions past 80% capacity then this can occur and there are no good
defragmenters since it is not usually a problem. So don't do it.

You won't require much space for the apps which are installed to root. I
have everything possible installed and I use just over 11 GBs. Most of the
space is used for tmp files and caches.

You can go with a single partition which is simpler up front but more time
consuming in the end. If you need to re-install then having a separate home
partition is a big time and nerve saver because you can do it while
preserving your data and settings. If you go with one partition then you
need to back up home each time.

To get more than one partition then you need to do a manual installation.

Create any partitions for Linux after Windows and you are less likely to
mess up Windows. You will need to use the partition manager or editor to do
this. First you need to make sure partions are unmounted. Then re-size
Windows smaller by 40 GBs. Create your partitions in the unused space freed
up by resizing. It is easier than it sounds.

Then right click on the partition that you want to install root on and
choose to edit it. Then choose to use it and choose the format (ext3 or
ext4) and mount point (/). Do the same for home but set the mount point as
/home. The first time you do this you will choose to format it but on
re-installtions you choose to use, but NEVER format it. Swap space is just
selected and choose to use it as swap/

When you choose your user name you will use the same user name every time
you re-install and it will re-use your home directory and preserve data and
settings.