Can I Bluetooth tether my Android to iPhone?
You won't be able to use BT-DUN on the streak unless there is something custom built into the UI.  My Archos 70 has a setting baked into Android for Bluetooth Tethering specifically.  Without that or some app to enable it, the Streak won't know where to get the internet connection from, even if the devices are connected.  Don't bother with PDANet because it only works when you are going the other way, sharing your Android internet connection with another device.  

Another option, would be to put MyWi on your iPhone and make it a wireless access point, then you can connect to it via your wifi connection.  There is one problem: the MyWi creates an adhoc connection and Android doesn't recognize adhoc.  You can get around this by editing your wpa_supplicant file but you need to be rooted to do this.  Here are the instructions to do this: http://android.modaco.com/content/dell-streak-streak-modaco-com/316049/ad-hoc-network-connection-for-streak/