Are there any good 2.3x tutorials on UV-mapping? I’m espescially looking for a tutorial that explains how to make the UV-mapped texture appear in the render (like this one, 6th page). I can’t find the “assign” button described in the tutorial.
You need to have a material assigned to the model. If you don’t have a material assigned to the object, with the object selected, press F5 and then click the Add New button. To insure that the material is assigned to all faces, press TABKEY to enter EditMode on the object, select all the vertices with the AKEY (maybe have to press a few times to get all vertices selected), press F9 to get Editing buttons up and in the Link and Materials panel, click the big Assign button.
Now back on the materials buttons (F5), click on the TexFace button. This will force the image you have mapped to the faces to replace the color on the material. Optionally, you can use a Texture channel to do more or less the same thing, but this is the simplest way to do it.
This question has been asked recently also, there should be other threads discussing it if you need more help.
Is it possible to apply a material to a face or a couple of faces? Or do I have to make new objects for everything that needs another texture?
Yep, check the Material Indices tutorial from the reblended tutorials.
Those tutorials are a bit dated and done with the pre-2.3x UI, but it isn’t hard to map them to the current UI. Also, the documentation at blender.org covers the basics of blender pretty well. When its finally updated with the release of the new book coming out, it should be very complete.
Yes I’ve ordered the manual and I had decided to wait for the manual, but as it’s gonna take some longer I decided I would start allready and try.
EDIT: I’m sorry but I can’t figure it out. I seem only to be able to add a material but then the 1 Mat: 1 won’t change into 2 Mat: 2, wich is what I can gather form that tutorial you sent me to to be the result. :-?
http://www.linuxgraphic.org/section3d/blender/pages/didacticiels/blender_material/tp2-index-ang.html
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Here is my try, Thats a good tutorial, very clear.
OOPS!
OOPS again? 
Fligh’s tutorial is really helpfull, but please try to post yours again ndnchief, the more tutorials the better.
Here, you might as well try my UV mapping tutorial too. 
https://blenderartists.org/forum/viewtopic.php?t=19378