HCl's Prophecy Enhancement Pack is a super cool thing. It runs WCP in high resolution, adds online multiplayer, allows DVD quality videos to be patched in and fixes bugs that were part of the original game. Recently, as adoption of Windows Vista has gradually increased, a small number of people reported problems running the upgrade's high res installer. HCl has investigated the issue and developed a workaround. If you have experienced crashes while running install.exe in the Enhancement Pack, unzip install_gui.exe into the game folder and run it instead. Be sure to report your results afterwards to help make future improvements even better.
Here is a fix for the High-Res patch installer. It should solve a crash which is most common on Windows Vista, but may also occur on XP in certain circumstances. If you are experiencing trouble running the regular installer, give this fix a try and let me know if it solves the problem for you.