Well... if you're willing to set up USB Networking and Samba, you can play your games, emulators, etc, from a shared folder on your computer, but you'll be tied to the computer by a USB cable.
There's 64MB of NAND memory, but only 50MB is available and you can run some things from it, but I wouldn't recommend.
An SD card is kind of important... even if you go pick up a cheap 128MB card at Walmart, you'll be able to enjoy your 2X more.