The text installer certainly lets you choose the partitions you want to use.
Since you are more at ease with graphical interfaces, you can boot Trisquel's
default (not NetInstall) live system. It contains an application called
GParted, which allows you to shrink Windows' partition (that, before, you
should defrag from Windows), an create in the free space partitions for the
subsequent Trisquel install. Here is a screenshot of GParted:
https://trisquel.info/files/Screenshot%20from%202015-10-21%2007_35_49.png
I suggest:
a swap partition whose size equals that of of your RAM (especially if you
want to hibernate the system, otherwise it can be much smaller, like 1 or 2
GB),
a 24 GB ext4 filesystem for the root partition (i.e., the filesystem that
will be mounted at /),
an XFS filesystem that takes up all the remaining space for user data (i.e.,
the filesystem that will be mounted at /home).
That partition schema (including the type of filesystems) looks like that of
the default install but I suggested more space for / (although I understand
you want a lightweight system, you may want to install some heavy
applications in the future, and you will not be able to easily enlarge a
partition at the detriment of the XFS one because XFS cannot be shrunk). One
the partitions prepared, you can reboot, run the text installer and, in that
installer, specify what are the partitions for / and /home (double check that
you do not specify another partition... and back up the data of the Windows
users before all that anyway!).
