[NTJedi]

Have you played the DOM_2 demo ? This will help you get a feel for the game... and it convinced me to buy the game.

Once I bought the game I played several maps until I felt knowledgeable about spells, units and nations. Depending on your tastes you'll find some nations more fun and effective. There's a good chance you'll lose the first half-dozen games. Eventually you'll discover AI weaknesses allowing you to win the majority of games.
At this stage you'll want to make the game more challenging by editing the .map file. The first and easiest change is by making them allies, but since you don't have the game yet this step is many months away.

The full game installs a Dominions\Docs directory which has a guide for editing the map file... the mapedit.pdf. Only make these changes once you feel comfortable winning and you're looking for a greater challenge against the AI.