Maemo is based upon Debian and, thus, uses apt to install software. The space your loosing is due to the .deb installation files being downloaded and kept in memory. These files are kept in the /etc/apt/cache directory. There are a few methods that can be used to get rid of these files, as they aren't needed after the programs are installed, not least of which is simply navigating to the directory and deleting them.

Here's a method I use in ubuntu to free space and it works in maemo also. (you'll have to have a program installed to use the root function. I use "sudser". I believe it's in the standard repos.)

Open a terminal and run these three commands (without quotes), upon the completion of each previous command:

sudo apt-get autoclean
sudo apt-get autoremove
sudo apt-get clean

Doing so will remove any "left over" dependancies that weren't removed (or are no longer needed) due to the removal of programs and clean the downloaded cache of installed applications. Doing so has freed up 97.1 mb on my own system. I hope it helps you do the same.