A few guildies and I were fed up with Baradin Hold PuGs one day and decided to try and kill Alizabal with just the five of us.

Doing Alizabal with 5 people actually makes the fight that much more interesting to do and it increases the loot per player.
Because Seething Hate will only spread over 5 people, everyone will take twice the damage and the healing will be quite intense because of it.

We've both experimented with a setup of 1 tank, 1 healer and 3 dps and (as seen in the video) with the setup of 2 tanks, 1 healer and 2 dps.
With only 2 dps Alizabal's enrage becomes a serious issue and you'll have to do all you can to put out as much dps you can. This also goes for the tanks - for the kill, we had our paladin reforge into hit and expertise.
If you're going with a 2 tank setup, there is little change for them. If you want to try with just 1 tank, you will have to make sure to have a dps taunt 1-2 seconds before Alizabal will cast Skewer. Directly after this dps gets stunned, the tank should taunt to get back the aggro. The goal of this is to have a dps eat all Skewers, while the tank takes all the melee hits. It should be noted, however, that this dps will be stunned approximately half of the effective dps time, thus greatly decrease his damage potential.

The song used in this vid is called 'Painkiller' by 'Red House Glory'. Check them out on YouTube, they're a great new band!