I tried the official way. This is the problem I encountered:
When I get to http://repository.maemo.org/; I observed that there are subfolders there. I selected http://repository.maemo.org/stable/bora. In that subfolder I installed
http://repository.maemo.org/stable/b...inaries_3.2.sh
By chance, clicking on it, the rest is done automatically as in PC. That is, the application is installed at the documents directory of the n800.
Real problem started when I connect to http://repository.maemo.org/extras/
It has many many subfolders and subsubsubfolders. I am lost. What should I do? Which files should I install? Many thanks to those who spend time for answering.

The best site I've found for up to date application and repository information is http://www.gronmayer.com/it then select your OS version and start clicking on the links which will install the repository into your application manager - Gnumeric's repository is listed here, which I've been able to install perfectly into my 770 running OS2007HE.

I don't see gnumeric under OS2008 downloads. Is it not available yet, or will the OS2007 version work?

There's a beta version,

Repository: http://people.debian.org/~tschmidt/maemo/chinook
Distribution: /
Components:

There's a thread on it, look for it. It mostly works, but it still has some serious problems.

--Denis

If by "this" you mean Gnumeric, then I have tried and see nothing crazy about it, it works fine.