Is there an online help for translating Greek participles into English?

I'm afraid not. I tried Perseus for "ontes" and after 10 min I gave up. You must have some familiarity with Greek and be able to recognise basic forms of verbs. See this page from www.ellopos.net/elpenor/lessons/lesson2b.asp?pg=2">Elpenor's 2nd lesson in ancient Greek, about such difficulties. Also try www.thefreewindows.com/?p=17">a freeware program that conjugates Greek verbs. It won't help much in your case, but it is the closest possible help I can find for the moment. If you discover anything else, please let us know.

Well, you can have a look to the AUSFUERLICHE GRAMMATIK DER GRIECHISCHEN SPRACHE, by Raphael Kuehner and Bernhard Gerth, Zweiter Teil, Zweiter Band, the paragraphs related to participles are Nr 480 to 496. It is in German and you can find it on the WEB at Perseus. Otherwiwe, there are fine books, particularly the GRAMMATICI GRAECI ed. Georg Olms Verlag, only in Greek with introduction and comments in Latin.