Already discussed to death, but...

True resistive multitouch requires a specialized resistive touchscreen/controller, it won't work on every resistive touch screen.

Some software trickery can be done to fake multitouch on existing hardware, but I've not seen any implementations that would perform well and reliably (other than for very simple demo purposes).

Unless you're willing to spend time programming the fake multitouch implementations for fun, just forget about multitouch on the N900.