Download Quake 2 (I got mine off of steam)

Go to your quake2 install directory on your pc, inside the baseq2 folder.

Make a baseq2 folder on your n900 plugged into the pc and copy pak0.pak, pak1.pak, pak2.pak to your n900 in mass storage mode.

Unplug your n900 from your pc and then open xterm. Type the following:
mv MyDocs/baseq2/pak0.pak .quake2/baseq2/
mv MyDocs/baseq2/pak1.pak .quake2/baseq2/
mv MyDocs/baseq2/pak2.pak .quake2/baseq2/