How to learn epic spells...

[xwarren]

If I understand correctly: a lvl 10 bard, lvl 4 fighter, lvl 10 sublime chord with the feat Practiced Spellcaster (Bard) can have epic spells?

Yes.

And what if instead of lvl 4 fighter the build has another spellcasting class. For example a sorceror? Is the caster level then determined by the highest class: bard + feat practiced spellcaster bard + sublime chord?

By default sublime chords levels stack with your highest arcane casting class, but there is a switch to change that if you want - 'PRC_CASTERLEVEL_FIRST_CLASS_RULE' - set it to 1 and bonus caster levels form prestige classes will be added to your first casting class.