I have to tell you, 300 MB HDD free or whatever is simply not enough to run OSX. All OSX programs use Virtual Memory (VM) which is memory temporarily stored on the Hard disk drive instead of in ram. Even OSX system requires some VM also. You either need an xtra internal or external HDD or backup some of the files onto cd/dvd-r/rw so you have more space available. I should imagine a no. of your programs, particularly any graphic programs might also have difficulty running.

Ok so I understand you're using an old mac, but something has to give to allow your OSX programs the freedom to operate normally without being squeezed continually by lack of HDD space. BTW not a bad speed for a G3, I have a G4 at only 400 MHz. lol (But not the one I generally use.)
I'm purely speaking from the standpoint of the health of running your system. I know this is probably a difficult issue to consider. I've had same problem on older macs with limited space.