Ouch. First and foremost, I'm not sure how this situation should be dealt with on Maemo so take my ramblings with grain of salt and proceed at your own peril. In any case, I'd start by rebooting the device and then trying to running application manager to "check for updates". Rebooting may delete some temporary files and free just enough space to resolve the issue. These files can be deleted without rebooting the device but rebooting is the easiest method to explain.

If that simple snake-oil remedy won't work and you feel adventurous and lucky, well, here's what I'd do on full-blown Debian installation. Note that you'll have to close Application Manager to run the commands on the terminal. If you read beyond this point you can only blame yourself if you get yourself into even worse trouble. ;-) Actually, if you can show your device to someone familiar with Debian ask him. He should know how to resolve this.

- Open terminal
- Check apt's cache size: du -sh /var/cache/apt/archives
- If there's anything at all in the cache, empty the cache as root: rm /var/cache/apt/archives/*.deb

After this there should be free disk space for apt and dpkg to play with. On Maemo, I'd then try to "check for updates" again. If this would still return errors (check the log), here's how I would continue on command line (after closing Application Manager):

- Try to configure partiall installed packages: dpkg --configure --pending

If Application Manger still won't work:

- Have apt-get to fix the installation: apt-get -f install

Be warned that "apt-get -f install" may do seemingly unexpected things such as install and/or remove packages.