Ubuntu performance on a VirtualBox

Ubuntu performance on a VirtualBox

I installed Ubuntu 13.04 on a VirtualBox on Windows 7 host. The problem is
that the UI lags a lot. I already installed Guest Additions and etc and
enabled 3D acceleration, though it made things faster it's still not
running smooth. I already have Ubuntu installed on this machine as
dual-boot so I have an example for how smooth the system should run.
Is there some configuration that should run Ubuntu smoothly?
Here are some specs:
Host machine:
Windows 7 64 bit
4GB RAM
Nvidia 9600GT
QuadCore Q8300 2.50GHz
Guest machine:
Ubuntu 13.04 64bit
1GB RAM
2 Processor cores
8 GB Space
3D accelartion enabled