Help! Problem installing OS X

[TonVanHest]

At last I have my Cube, It looked very dirty but it worked. While my 
wife cleaned the outer shell I exchanged the memory for 256Mb and the 
HD with a 120Gb.

So I expected to be ready and put in my (regularly bought) OS X 10.3 
insyall disk1. First I partitioned and formatted the HD and then went 
thru all the windows containing usual warnings until I came to the one 
where I could select the HD on which the OS should be installed.

To my shock, I was not allowed to install on my new disk!!

Repowered on and tried again, same problem. I could not install the OS.

So what is wrong here?

(I also powered the Cube in targetmode and then I can copy data tot the 
new disk. So the disk itself is in order. But I prefer a full clean 
install)

Help is very much appreciated!