I would definitely recommend to either make sure that you friend has at hand a trusted media with which he/she could reinstall Windows
if he/she ever wants to, or even better do not erase Windows
but configure a "dual boot" Windows / Linux on his/her computer.
To do that:
1) Get gparted
. For that I recommend dowloading and burning a live cd
2) After having made a backup of all valuable data
, use gparted to downsize the Windows partition(s), in such way that you keep only around 10 free gigabytes inside that partition.
3) Then with gparted reuse the freed disk space to make three Linux partitions:
- the first of around 20 gigabytes for /, formatted as Linux, e.g. ext3 filesystem
- the second of the RAM size for swap, formatted as Linux Swap filesystem
- the third using the remaining disk space for /home formatted as Linux, e.g. ext3 filesystem
Be careful while using gparted : do not interrupt it while it is running
, knowing that some operations -- noticeably resizing -- can take a lot of time.
After that you will be able to install any recent distribution, instructing the installer to configure a dual-boot Windows / Linux, using the already prepared partitions as stated above for Linux.