Choppy video and sluggish computer response

I have an iBook G4, 1.07 gHz, 1.25 gb RAM computer, running os x 10.3.9.

Sometimes the computer is very unresponsive. If I try to type, say into the search box on the firefox browser winder, the computer gets very congested, and it takes several seconds to display what I have typed. If I try to make other changes, like click or move the cursor, visualization of those changes is also delayed.

This problem seems to improve if I restart my computer, and it seems to get worse the longer I keep my computer on or if the battery had been turned off due to a loss of power (my battery connection fails sometimes if I move my computer around).

This problem also improved for a short period of time when I upgraded my RAM to 768 mb to 1.25 gb, but now it is bad again.

I have noticed recently that streaming video is also choppy now. This problem happens constantly: the video is choppy, but the sound is fine...eventually the audio and video become out of sync. I used to be able to stream videos with no quality problems.

Does this sound like a hard drive issue? I have an extra harddrive at home I could put in, but I want to make sure this might be a problem before I go through the effort to swap it out.