For your light:
A few BlenderArtists got annoyed at the fact that paths don’t work in the game engine so we hacked together a solution:
This will ‘bake’ a path animation to an Ipo. The Ipo can be used in the game engine by attaching the Ipo data block to an object and using an Ipo actuator in the logic bricks and setting it to play, loop stop or loop end depending on the behaviour that you want.
The scripts posted towards the end of the thread, particularly the version by sanne, are very useful.
I’ve since found a couple of bugs but not yet changed the script. These bugs are relatively minor and only really apply when the Ipo is to be repeated precisely. They can also be corrected by manually editing the generated Ipo curves.
One bug is that the Ipo starts on frame 0 rather than frame 1 (if memory serves me correctly) so the Ipo curves need to be selected and shifted 1 frame to the right.
Another is that the first frame needs to be duplicated and added to the end to enable proper looping without a jerk because of the missing frame.
The final bug occurs only when partial frames are used (using the frame property) and is due to the flipping of Euler rotation curves. This final bug can be fixed with an Ipo cleaner script or by manually selecting the offending points on the curve and translating them on the y axis in the Ipo curve editor by 36 units(360 degrees).
Not sure if you know this, but it’s worth noting that only spot lights will cast realtime shadows in the game engine (GLSL mode). It might be possible to achieve interesting results by baking the shadows of all static lights to textures and having your movable light a spot light with a wide range.
This is possible using the videotexture feature for animated reflection on near-planar surfaces (Mirrors, water etc.). There are several tutorials about.
Alternatively, if you have complex objects that require reflection, martinsh wrote a GLSL shader that can apply an environment map to static objects as reflection. This can be found in the game engine forums somewhere.
Unfortunately, animated reflections on complex objects are tricky (impossible?) to achieve right now because the game engine is incapable of rendering an environment map from one camera whilst rendering a standard screen view from another camera. Environment map rendering is possible but is in the game framing settings menu that are global and affect all cameras in a scene.
General use of Ipos in the game engine:
The Ipo data block needs to be linked to the object in Blender.
The object needs a logic setup that contains an Ipo actuator to enable the Ipo to be played.
I hope this sheds some light on your issues.