Question: It is often said that Nibbana is unconditioned. But isn't Nibbana to be attained through practice of the Noble Eightfold Path (abandoning desire, meditation, realizing paticcasamuppada etc)? Aren't those practices conditions for Nibbana? What am I missing here :) ?

Answer: 
The practice of the eightfold noble path leads to the *experience* of nibbāna, just like the act of adverting the mind to the eye door leads to seeing light. Light, the object of seeing, is saṅkhata (conditioned), but nibbāna, the object of supermundane consciousness, is asaṅkhata (unconditioned). So nibbāna isn't the result of the eightfold noble path, the experience of it is.
I see two ambiguities here which might be the responsible for the confusion.

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> with the six sense bases as condition, contact;
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> -- SN 12:1
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The above is one link of conditioned arising chain, which explain how many things are conditioned. Would it be correct to, according to the above, conclude that the six senses *cause* (or produce) contact? That would be awkward.

This quote means that if a "contact experience" is present, then the corresponding sense is present. A more verbose reading of the above would be "six sense bases are a supporting condition for contact". 

As another (unrelated to buddhism, and perhaps poorly chosen) example, if you study, you become more knowledgeable. But your knowledge, at any given point, is not constituted by "studies". There is an ambiguity in how we can interpret "conditioned". Conditioned ≠ caused by. 

The matter in question is that it is more a statement about a ["necessary condition"](https://en.wikipedia.org/wiki/Necessity_and_sufficiency) than a statement about a particular cause.

There is also another ambiguity in play here. Nibbāna is unconditioned in the sense that **it** has no supporting condition. Echoing [yuttadhammo's answer](https://buddhism.stackexchange.com/a/9083/382), nibbāna is "one thing" and the experience of attaining nibbāna (which requires all the proverbial effort) is "something else".