I've installed gjiten without a problem using apt from command line, not the Application Manager GUI.

Here is a small howto for those who don't know what I meant above.
Intro:
Apt is a Debian package management system and os2008 is of course Debian based. The Application Manager is a front end to apt. Apt does all the installation but in difference to the graphical counterpart it doesn't complain as much.

Here it goes:
1. Check that you have the repository.
Open Application Manager. In the menu go Tools -> Application catalogue.
If you attempted to intall it earlier than you should find gjiten catalogue in the list,
else add it manually. It should contain:
Name: gjiten (you can choose any)
Web address: http://gjiten.garage.maemo.org
Distribution: chinook
Components: user
Close and let it refresh if it asks too.

2. Install becomeroot package http://eko.one.pl/maemo/dists/bora/u....1-2_armel.deb
using the aplication manager.

3. Close aplication manager and open xterm (in Utilities menu).
Become root with:
sudo gainroot

Install gjiten with:
apt-get install gjiten

After executing this command you need to agree with all questions by entering 'y'.

If that succeeded then you have gjiten installed and should find it in the menu with other apps.

A couple hints on using apt.
To search for packages use command:
apt-cache search name
where name is what you look for.
To refresh to package list:
apt-get update

I hope that helps.