Google "archive team maemo". There you will find N900 unlocked images from skeiron archives. There is a link. Choose pr 1.3 global. You need also the flasher to flash your phone. You can google flashing N900 and will find instructions. Then from the forum check cssu thread (community updates). I suggest choosing the cssu testing version. I suggest you add to your repositories this:
http://repository.maemo.org/extras/
fremantle-1.3
free non-free

Also in cssu instructions there are other repositories old what you need. There is no real support stuff here except the members. There are no updates for security so your phone will not be updated for security. Your browser wont open all the pages you probably want.

Check also instructions "Perfect setup for N900". For updated browser you need to install Easy Debian and for that have outdated
Debian image for N900 and then you can have netsurf 3.8 browser which is fast but I think it wont play videos or open all links.

And before you post questions and start new threads read everything from maemo wiki and you learn a lot how things work here. Have fun with your phone. There is an effort for an updated maemo version called leste but it is not ready yet.