To start, just figure out the mechanics of being able to play the game inside the emulator. I haven't done a TAS of a Windows game, so I don't know which of BizHawk+DOSBox / PCem+LibTAS is better/easier, but maybe someone else can offer advice. If the game can run in Windows 95/98, then it looks like
either choice will work, but for Windows XP you'll need to use PCem.
Once you have the game running, you can practice recording a movie and using savestates by playing casually, or for example at 50% speed for better control. You can share work-in-progress movies at
Userfiles, even if they are incomplete or unoptimized.
Then begins the long process of building the TAS, learning and documenting the game's speed tricks, and using savestates to find the fastest way to do every action. See
Wiki: TasingGuide for general guidance. My advice is to post updates when you've made progress and ask questions if you get stuck.
Post #453276 has some links to VODs/livestreams if you want to see how people approach the process of TASing.