I have a eeePC 900 and installed gOs which I think is what you are referring to as GoogleOS. The G does not stand for Google, but Good.
My eeePC triple boots. I kept Xandros on the smaller 8 GB partition and installed Windows XP on the 12 GB partition. I installed gOS to a SD card. Instructions for installing new OSes can be found at wiki.eeeuser.com. Problems that you are likely to encounter are overwriting the boot sector for the eeepc and thereby preventing Xandros from booting. You can download a copy of eeepc.bin here:
http://www.3eportal.com/downloads/. This will allow you to re-write for booot sector back to its factory setting (just in case).
You can avoid boot sector problems by writing grub to the partition or card instead of the master boot sector. I am not sure if I can remember how I did this for gOS, but in Ubuntu it is done on the last stage before installation where the changes are reviewed. Just click on the Advanced button at the bottom and choose the device where gOS or Ubuntu is installed (not sda or sdb unless that is where you installed it).
You will need to do two extra things. You will have to press Esc on boot up to get into the boot menu and you will have to edit grub (menu.lst) so that it points to (hd0,0) instead of what it says. You can do that temporarily by pressing e to edit on that line, making the changes and then pressing enter and b plus enter again to boot. So that you don't have to do this every time edit grub with sudo gedit /boot/grub/menu.lst.