A lot more information is required but we'll do the best with what we have.
What OS are you running? How much RAM do you have installed? How often do you restart the machine.
First thing to try is to go to the Disk Utilities and run the Disk First Aid and Repair Disk permissions. Next, in the same place, verify the disk. You will not be able to fix any problems found but it will be a starting point.
If it does find problems, you will have to start from the OS X CD and run Disk utility from there.
Download and install a free program called Yasu, Google for it, and run the utilities that it contains.
Note that Firefox has a memory leak problem and it will gradually use up ALL available memory in your machine. Lack of memory will cause the symptoms that you describe. To reclaim the memory, restart the machine.
What, if any, Disk Utilities do you own? I recommend Disk Warrior and TechTool Pro to begin with, in that order.
Hope this helps
i have a 800 MHz, 256 MB ibook G4 that i bought almost 2 years ago. i've noticed recently that it's been slowing down quite a bit, and i can barely have two applications running without the little rainbow wheel showing up. i often have to force applications to quit or the application quits on me. this seems to happen more frequently when i'm on the web, even though i have DSL and this never happened before.
one thing that has been different is that i have downloaded firefox and that's what i normally use. when i view the file info for my hard drive it says that i have 27.94 GB of capacity, 17 GB available and 11 GB used on disk.
any suggestions for how i can get my ibook running smooth again? thanks.