Can you use a magical item to satisfy feat or ability prerequisites?

[DreamGoddessLindsey]

Like the topic title says. For instance, if I have 15 DEX and use a Belt of Incredible Dexterity +4 to make that 19, am I able to take Greater Two-Weapon Fighting? Which, of course, means I lose access to that feat any time I take off the item and my DEX dips back below 19. Not just for feats, though, but anything that has a prerequisite that you can pretty much permanently have with a magical item. If I'm a wizard with a 15 INT, can I cast 9th-level spells as long as I keep a Headband of Vast Intellect +4 on?

I would think that I could, again losing the feat or ability if I take the item of, but I'm not entirely sure.

[Quatar]

Yes, once you wear those items for 24 hours the bonus counts as a permanent bonus.

[Midnight_Angel]

You can.
However, if you lose access to the bonus, you lose access to the ability, just as you stated.
Note you won't have to take the item off for being able to lose the bonus (Dispel Magic, Antimagic Field and Disjunction come to mind)...