GMJCZP,
As a recommendation, I suggest you forget NotePad (standard) and right click and select "Open With" to maybe PsPad or NotePad+ (NotePadPlus),
which both supports Edit of Avisynth script (with keyword hi-lite) and Play of the script, really quite a lot more useful than NotePad standard.
As Pinterf mentions in Avs Usage, MPlayer2 is still supplied, even in Win10, I always quite hated WMVxxx, really horrible, whereas MPlayer2 is very
usable and what I use (together with MPC-HC in PsPad) to view/test scripts.
Give'it a whirl, you might like it.
EDIT:
You can actually set that inside both PsPad and NotePad+ settings.
EDIT: In XP, some clips do not play in MPlayer2.exe, but for most, I much prefer over WMVxxx.
In XP, MPlayer2, is located in same directory as WMVxx (C:\Program Files\Windows Media Player\).
EDIT: It is a bit peculiar that MPlayer2 is still provided, another weird little thing is that from W98 onwards, there was always
a DVD player included (
REALLY basic) , just not an MPEG2 decoder, called DVDPlay.exe (I think, in system32), dont know if it is still there.