Then you'll have to wait for a custom rom available through ROM Manager. Technically their is a way to install the same thing you can run off the SD card onto your internal memory, but you run a greater risk of causing problems for yourself.
My understanding is that we'll be seeing the Nookie Froyo available as a flashable ROM in the next couple days (that's a blind guess, but it doesn't sound like it's far off)... I'd wait until then, because it sounds like that is exactly what you're looking for.