In the lessons on this site it says that two vowels together are not allowed in turkish. But when i started to learn some words from a teach yourself turkish book it said certainly means tabii (two vowels together) i looked it up in the dictionary incase it was a typing error and it also says ´tabii´. Is it just when a suffix is added when two vowels cant be together ? :S

Exceptions are words loan from other languages.

Hmm.. as far as I know, this rule is only valid for Turkish-rooted words.  And tabii is not a Turkish word as far as I am concerned=)(according to the turkish language society´s dictionary, it is an Arabic-rooted word).. its equivalent in Turkish is "doğal".

but you may have meant "tabi" as in "tabi ki".. but it is written with only one "i".. it is a common typing mistake..

 İts written ´Tabii ki´  with double i as far as i know..

e.g. saat

And ´haavalani´.

 There isnt any ´haavalanı´ but ´ havaalanı´

Ohh ok thanks everyone!

And maalesef - meaning - unfortunately 

Oh and be careful of words like meşgul as if you look carefully you´ll see that it´s letters aren´t following vowel harmony, and meşgul tripped me up once before when adding a suffix

here ---> T-E lutfen

I was just going to say that!

This is an example of a composite noun (two words joined together) which are exceptions to the ´no two vowels together´ rule. (hava alani)