u need to give a partition for root which is denoted by "/" and a swap partition of around 500 MB or less in the installer gui.what the installer trying is to auto enable mounting of ur windows(?) partitions in ubuntu.Linux FS are ext3 which is used.
read below article.its for u:
New to Ubuntu 7.04?
https://help.ubuntu.com/7.04/newtoubuntu/C/index.html
for P-I like systems try a distro called Antix based on simplymepis.