Monsters as Epic Characters
As first introduced in the forgotten Realms Campaign Setting (and discussed in detail in Savage Species), the efective character level (ECL) of any creature more powerful then the standard races in the Player's Handbook is equal to the creature's Hit Dice and class levels (if any) plus it's level adjustment. This replaces the rule in the Monster Manual that states that a creature's "monster level" is equal to it's Hit Dice.
Regardless of it's ECL, a amonster with class levels uses the base attack bonus and base save bonus pregressions of it's class (rather then the pregression shown on Table 1-1) until it has 20 character levels. Beginning with its 12st character level, it uses the pregressions shown on Table 1-1.
In any other place in this book where 'character level' is indicated, you can use effective character level instead. For example, a creature with a level adjustment of +5 who is also a 13th-level fighter/3rd-level blackguard is ECL 21 and elegible to select an epic feat provided he meets the prerequisites.
Savage Species has level adjustments for most monsters in the Monster Manual. Use these modifiers to estimate appropriate modifiers for other nonstandard PC races that you might choose to include.