I was wondering if there's also some sort of guide to tech-tree "builds", that analyses in more detail why and how to get to certain techs how fast, depending on the situation.
tried search but didn't find anything. maybe one of you can point me to something like a "complete idiot's guide to the tech tree or how I stopped worrying and love the bomb"
This won't really help you tech faster, but it is an idiots guide to the tech tree that I created for my own use. It helps me decide what to tech towards or trade for (the annoying thing about tech trades offered by the AI is that you can't open the tech tree during the negotiation

)
Civ4 key techs.
First to it gets Free stuff:
Music (free GA)
Liberalism (free technology)
Economics (free GM)
Physics (free GS)
Communism (free GSpy)
Fascism (free GG)
Fusion (free GE)
Religions founded:
Meditation
Polytheism
Monotheism
Code of Laws
Philosophy
Theology
Divine Right
Corporations Foundable: Corporation PLUS
Railroad + Engineer = Mining Inc (hammer bonus, consumes Gold/Silver/Coal/Iron/Copper)
Medicine + Merchant = Sid's Sushi (food and culture bonus, consumes Fish/Crab/Clam/Rice)
Combustion + Engineer = Creative Constructions (hammer and commerce bonus, consumes Iron/Copper/Aluminum/Marble/Stone)
Refrigeration + Merchant = Cereal Mills (food bonus, consumes Wheat/Corn/Rice)
Rocketry + Scientist = Aluminium Co (creates aluminium and science bonus, consumes coal)
Mass Media + Artist = Civilized Jewelers (cash and culture bonus, consumes Gold/Silver/Gems)
Plastics + Scientist = Standard Ethanol (creates oil and science bonus, consumes Corn/Rice/Sugar)
Obsoleting techs:
Economics - Castle
Rifling - Walls, Chichen Itza
Corporation - Great Lighthouse
Astronomy - Monument, Stonehenge, Colossus
Steam Power - Hagia Sophia
Scientific Method - Great Library, Parthenon, Temple of Artemis, Monastery
Combustion - Whale
Industrialization - Ivory
Plastics - Fur
Computers - Angkor Wat, Spiral Minaret, University of Sankore
Mass Media - Apostolic Palace
Advanced Flight - Stable
Fibre Optics - Kremlin
Other:
Mathematics - +50% chopping yield
Currency - +1 trade routes
Civil Service - farms spread irrigation
Guilds - +1 hammer workshop
Printing Press - +1 commerce villages/towns
Replaceable Parts - +1 hammer windmill/watermill
Corporation - obsoletes Great Lighthouse but +1 trade routes/city
Chemistry - +1 hammer workshop
Biology - +1 food farms
Electricity - +1 commerce windmill, +2 commerce watermill
Satellites - reveals map
Genetics - +3 health in all cities
Future Tech - +1health/+1happy in all cities
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Obviously, I've left out some stuff (like the enabling techs for Oracle, or Representation, etc.) but I find this helps me plan my tech path, wonder/unit builds, and so on.