I have Ubuntu 8.1 dual-booting on my Aspire one. The easiest way is to
use a computer with CD drive and boot from the Ubuntu CD, then create
a thumb drive from there. Look under "System -> Create a USB startup
disk". I have been unable to create a workable USB disk on any but 1
GByte sticks, so you may have a problem with 2 GB or larger sticks.
Make sure the USB drive is formatted FAT16.

Set your netbook to boot from USB and install. I also had to install
madwifi to get the wireless working.

I found that xfce is a better fit for the netbook, so you might have
better results installing Xubuntu.