Sqad is right about the Koran not banning alcohol - it does ban pork etc. Indeed the Koran refers to the streams of alcohol flowing in heaven (never knew Scotland was heaven......). More seriously, the reason that it is on the forbidden list (haram) is that one should not be intoxicated for prayers and with those five times a day, it means essentially absolution.
The relevant parts are
Verse 4:43, in which Muslims are told that they must not pray while intoxicated. The real meaning is that any person shouldnt be drunk when he is in contact with the others. Because the real meaning of praying is " contact between people and between them and God" . Then the same verse gives the reason and which is to have control on your contact and talking.
Verse – 2:219 – which says that in wine and gambling "is great sin, and some profit, for men; but the sin is greater than the profit. Allah did not mention in that verse that alcohol is prohibited but it was an advice that " alkhamr" which exactly means to drink until you became anaesthetized can be dangerous. Also the same verse did not mention that its " Haram " which means prohibits, but it says that its better to stay away from to be drunk as anaesthetized .
Verse in 5:90-91, intoxicants and gambling are called "an abomination" and "Satan's handiwork": "Satan's plan is (but) to excite enmity and hatred between you, with intoxicants and gambling, and hinder you from the remembrance of Allah, and from prayer: will ye not then abstain?"
Hope this helps clear things up.......Sunnites (UAE majority tend to have a more liberal view of this than the stricter sects such as the Wahibis (Saudi) and, well known, the Shiites.