It would be a struggle, but if you do not expect to use very many plugins, it can be done. You will need more ram, but it is very cheap now - get as much as will fit into the computer.
Try to find an old version of ProTools Free, that will run in OS9.2.2. The latest recording software depends on a much faster computer.
You will be able to record 2 tracks at a time, and you might just be able to accumulate 16 tracks if you are very parsimonious with the plugs.
I used to run PTFree on my G3iMac 450mHz, and I am sure I had more than 16 tracks and no performance problems at all, using the Mac's built in sound card.
You will soon become addicted to recording by yourself, and will want more though!