http://www.abandonia.com/files/extra...Eye_Manual.zip
First of all you may challenge only other warriors. You can't get into a hand-to-hand battle with a bard or a druid. The success of such battle depends on
a) Arms and Ability attributes
b) The kind of weapon that your champion wields (Sword of Nuada is the best)
c) Might and Heroism skills.
Sometimes enemy hero will refuse just for the heck of it, then immediately challenge you for a duel in his turn.
EDIT:
No warez? Ok. Then I'll link to the same thing but on abandonia... duuuuh