Thanks for the replies.
I had an even older PC (15 years?) in my basement, and as a experiment, pulled the hard drive out of that (2 GB, I think) and installed it into my Dell Dimension. I am going to format and attempt to install Windows XP on this drive and see if I can use it until the new drive I orders arrives.
To this point, it has been a learning experience for me... I've learned how to remove the front case and plastic casing, as well as both hard drives from the respective computers and install the functioning, albeit old, hard drive in the newer computer. It's certainly a satisfying feeling to be able to do these type of things myself, and it's nice to have the option of attempting to fix/replace a hardware concern without having to rely on others.
I will likely order the hard drive referenced in this thread. So far, the old hard drive I installed appears to work, and while I don't expect much in terms of using it, I am glad I got the experience from learning how to remove and install a hard drive from my computer.
If anyone ends up searching for this thread as a result of having similar problems with their Dell Dimension 4100 hard drive, I came across a well written and diagramed guide that instructs how to remove the various casings and hardware so that one can remove/replace the hard drive itself. That guide can be found here:
Removing and Replacing Parts: Dell Dimension 4100 System Reference.