Hi,
Something I noticed a lot of people don't know about: the complete DoW Soulstorm/Dark Crusade bible. This is a fantastic peace of work that all serious players absolutely need to play this game to its fullest potential:
http://warhammer-game.narod.ru/wiki/Dawn_of_War_Players_Guide.html
Whenever you want to learn a new race, read through the entries. All of them! You'd be surprised what you will learn.
Happy gaming,
Valiant