So, We were recently fighting a "monster" wich was using a playable race (no LA) and had levels in druid. How does one calculate exp for this? I was also fighting a vampire, at what stage do you use CR increase for vampire template and when do you use LA? Of course both on Playable races/classes that we as a party are fighting
An NPC never cares about LA. Only CR determines experience rewards. Consult this question for how to figure out an NPC's CR.
As per Improving Monsters:
Most templates increase the creature’s Challenge Rating. A template might provide a modifier to be added to the base creature’s CR, or it might specify a range of modifiers depending on the base creature’s original Hit Dice or CR.
While an NPC technically does have an ECL (which is what LA is factored into), the NPC's ECL never matters. From reading the monster entries:
A character’s ECL affects the experience the character earns, the amount of experience the character must have before gaining a new level, and the character’s starting equipment.
An enemy NPC doesn't care about any of these things, since he doesn't earn XP nor level up.