i:0:"i/4.in"
d:{(,/x)@.=+/!2##x}                               / rotate matrix so the diagonal is straight
-1+#"XMAS"\" "/x,|'x:,/(i;+i;d i;d@|i)            / part 1: matches of XMAS in all flips, rotations
+/{("A"=x@4)&/160=+/x(0 2;8 6)}',/(,/'3':+)'3':i  / part 2: how many 3x3 windows are X-MASes

Not my proudest day... like usual, check out shadow's solution for some quality code!

For part 2, I use the addition to verify that each opposing corner is different:
 M.S
 .A.
 S.M
isn't a valid X-MAS.

~/aoc24k/4.html