First of all, please let me know if any of these assumptions are incorrect:

• You're running the PR1.2 firmware
• You haven't enabled the extras-testing or extras-devel repositories in the application manager
• You downloaded the portabase .deb file to the N900
• You tried to install the file by opening it with the file manager

If the above is all correct, you're using an uncommon method of installing software on the N900, but it should work (just tested it on my N900). Make sure that you've downloaded a .deb file with "armel" in the name and not "i386"; you should have downloaded this file.

If it still isn't working, then either your downloaded file is corrupt (the browser saved it as text, etc.) or something else odd is going on. You can try installing it from the command line, if you're comfortable with that, or you can enable extras-testing and install it directly from the application manager.

Are other people also having trouble installing PortaBase? It only has one vote in extras-testing so far, which is going to make it difficult to promote to extras...