Check out the threads concerning the OS.IMG.
Here's the gist of what to do (mainly copied & pasted from other's posts.)
It is easy of you have a copy of this on a CF Card (usually would have come with the netbook).
You can download it.
Download the OS from
http://www.psionteklogix.com/teknet/.../downloads.htm
(You'll need to register for free to Symbian)
and note that you must rename the .IMG file to OS.IMG for it to be recognised by the netBook. Put the file on a CF card.
Remove all batteries (backup and main) - this will reset the whole netbook.
Then replace backup & main battery after a few minutes. Turn Netbook on - it should ask for the OS on a CF card.
Slide the CF card in and all should be well.
Ask if you need any more help.