Well there is iFix it , you can google for it on how to open the iBook step-by-step with pictures.

The RAM is somewhat easier to upgrade. I suggest you to get one of those cheap rams , im using just fine. For HDDs , its somewhat difficult and tricky to upgrade. But its well worth the thing in the long run.

I prefer to keep the old HDD first , use carboncopycloner or CloneTool to clone back the HDD