I debated about whether to revive such an old post, but...
I brewed this, and I bought Hazelnut extract from Amoretti (http://amoretti.com/
) -- They have a "Hazelnut, Praline," that isn't listed on their website, which is what I bought. It has a great smell, and the beer tasted great at bottling time. I'll let you know how it is after it carbs up.
For anyone who gets that extract, I tried two different volumes, 20ml and 10ml (in 5 gallons - This was a 10-gallon batch). l'll let you know how it turns out, but right now my impression is that 20ml was too much.