To use iFile to install a deb, here is how I do it:
Download the .deb to your computer.
Open iFile on your ipod, and click on the WiFi logo on the bottom.
A page of text will display, with a url at the end, something like "http://192.168.xxx.xxx:10000".
Enter the url into the browser on your computer.
A root directory of your ipod will appear in the browser, with an upload box.
Use the upload box to put the .deb somewhere on your ipod, like in /tmp.
In iFile, tap Done and browse to the .deb, and tap it, then tap Installer in the menu. It should then install.