You can clone your OS either to the internal memory (2GB) or to a sd-card. Then your device will be set to boot from that device and all that memory will be available to you for system usage. Additionally you can set up a swap partition just like you would on any other Linux system. With that (and 256MB swap) I've never run out of memory ever. All these topics have been discussed on this forum in length and can be found using the forum search. (At least if not flooded by N900 theads...)