That can be solved by using the mIRC $cos and $sin functions. But, $cos and $sin require the value to be in radians, not degrees...

You can convert degree values to radians by multiplying the degrees by 0.017453 (which is pi / 180).

Say that %x1 and %y1 are the starting co-ordinates, %angle is the line's angle in degrees, %length is the line length... I'll use %x2 and %y2 as the ending co-ordinates:

set %x2 $calc(%x1 + %length * $sin(%angle * 0.017453))

set %y2 $calc(%y1 + %length * $cos(%angle * 0.017453))