The TI OMAP they use in the N800 and N810 has hw 3D acceleration, but TI never built the chip for a screen resolution of 800x480. So it isn't possible to get fullscreen hardware acceleration at full resolution. The other problem is that since the OMAP isn't built for 800x480, the screen is not connected to the OMAP directly. This is the cause for tearing and means that hw accelerated 3D wouldn't be as fast as desired.
Also, there exists no Linux driver for kernel 2.6 yet, and the producer doesn't seem to be interested in kernel 2.6 support. Only kernel 2.4 is supported as of now.
Maybe Nokia could do something about the missing kernel driver, but the hardware issues cannot be solved and we have to wait for the next-generation tablet.