There are "smatterings" here and there, but the most comprehensive site on the web is that hosted by Dr. Pierre Picouet. I will warn you that he uses a "multi-media" hosting service and there are pop-ups and ads galore. The site is "Los Tercios y el Ejército Español, 1525 - 1704", and it does offer English translations on the site. You can find it here:
Another decent source comes from the New York Public Library's digital library archive of the Vinhuijzen Collection of Military Uniforms, found here:
http://digitalgallery.nypl.org/nypldigi ... _id=269277
Simply select the nationality and then the time period within that nationality.
Probably the most exhaustive source on the Spanish, with a specific section on the Italian theater, is the excellent CD created by GianCarlo Boeri, José Luis Mirecki and José Palau, and titled, appropriately, "THE SPANISH ARMIES IN THE WAR OF THE LEAGUE OF AUGSBURG (NINE YEARS WAR 1688-1697)". You should be able to get this from either On Military Matters in the US or from Caliver in the UK, if not then Dan Schorr in the US still sells them as well. Excellent information plus full color plates and flags (where known).
Good luck with your project!