Apologies, if asked before. I didn't found anything; but then, how about divide this forum and make one for every Gothic game? Anyways...
I'm still at the very beginning, but am just curious if it's normal for the orcs around the rebel camp to ressurect after i beat them. As they're lying on the ground, regenerating, I can only grab the weapon and stuff they carry. Didn't I kill them properly enough or what?

You have to administer the 'coup de grace' to kill them -- stand next to them, hold down the right mouse button then press the left button.

Thanks for the answers. Think I'll can go on playing now.
Still curious, this means yellow-named orcs are not hostile enough? Because when thy get up, they no longer attack me.

Yep. If memory serves there are 5 colors to denote a character's status towards you. Blue indicates a companion that is following you (there are only a few of these in-game, like Diego, Gorn, etc); if I recall correctly blue NPCs can't be hit with any kind of friendly fire. Green indicates that the NPC is friendly towards you; an additional thing to note is that with green NPCs you don't have to worry about friendly fire with melee weapons unless you are directly targeting them (and the same goes for them not accidentally hitting you, something that's a big concern with white NPCs in large melee battles). White means an NPC is neutral towards you, and is the default for most NPCs in the game. Yellow means that an NPC isn't particularly happy with you, probably because you've beat the crap out of them at least once; if you beat them down a few more times a yellow NPC may turn red. And finally red NPCs are hostile towards you and any fight with them is a fight to the death.