Try again with KDE4!
OO has "evolved" too in the meantime.

I still have a similar machine under my desk (AMD K6-2 450MHz, 320MB RAM) and anything beyond a slim Xfce desktop is unuseable. Zenwalk (Xfce) was slow 5 years ago, Slax (KDE3) wasn't even done starting the desktop after 10 minutes.
I'm running a minimal Debian with a minimal LXDE on it which is ok if you're patient, nothing more, nothing less. For office I use Abiword/Gnumeric.

I'd say Easy Debian on my N900 (CSSU stable, 850MHz) has about 1.5 to 2 times the perfomance of this ancient PC.

There's still SHR [1] which dos1 promised to get running on the Neo900. I think it's realistic since it's already running on the N900 [2] (with some constraints).

After having had a look at the SHR UI and some tests with Bodhi I think Debian with the Enlightenment desktop should be quite useable on the Neo900.
My biggest concerns at the moment are the kernel (in terms of power consumtion - my hopes are on freemangordon here), the stability of Enlightenment and the SHR software on Debian and finding suitable end-user software for the tiny screen.


[1] http://www.shr-project.org/trac
[2] http://www.shr-project.org/trac/wiki/Devices/NokiaN900