The core saturation depends on voltage x time, there is a universal transformer equation you can use to work out the primary turns, look here:
**broken link removed**
If you look at the datasheet for your core max flux density will be quoted Bmax, for powdered iron usually around 0.3 Tesla.
It isnt a question of how much power will a transformer take as far as saturation is concerned, transformer saturation is more likely to occur when the trans is unloaded as flux density within the core is highest with no load, despite what you might think logical.