You can choose to install GRUB in he MBR. This is the default choice and the simpler one (otherwise you may end up with two bootloaders after installing a second distributions).
/dev/sda1 must be the "restore system" (not sure to remember how it is named)
partition of Windows. /dev/sda2 is the Windows partition. You can delete
everything other partition from GParted (including in the Live system) and
relaunch the installer. As far as I remember, it will propose, among the
automatic partitioning schemes, the installation of Trisquel in the free
space.
