Honestly i would not go into modding to mutch , make only some usefull changes , like get new rounded cables ( only usefull if all your drives are running in ata 133), get new fans ( silent ones ) buy them very large, if you can replace the fan of your power block ( i dont think it s the most noisy one).
If your case is over heating , read a guide about air flow, basicaly, the best solution is to add in bottom front of your computer a fan the flow air inside, you should already have one top behind that push it outside.
Try to avoid to do like me , and do not struck alll your hard drives toghether( well i dont have enought room in my case to separate them).
What else , try to get ram with radio waves protection ( not sure it s callled like this), it s kinda usefull on modern computers ( especialy if you have a tuner tv card ). Putting the datas and the system into 2 separates partitions is already a good iddee but better place them into 2 differents hard drives.
Hard drives racks with fans are not usefull , honesly , it heat more with than witout them ( also the more fans are small , the more they are noisy , they have to rotate faster ).
Well , also if you have time to spend , do not even spend time modding , but try to install linux and play with it, you ll see , there s already plenty of intersting things to do with it.
