I seem to recall at one time making a folder containing hidden files, but I don't recall anything at all about it.
My hard drive is almost full so I need to purge some stuff.
How do I find those files? Do I just check "unhide" or did I end up password protecting them so they are lost (but taking up space) forever?

Hidden files/folders:
Double click on My Computer desktop icon.

Click on Tools menu - Folder options - View

Select Show hidden files and folders (if not selected already)

When you explore your file directories the hidden folders will be a lighter ghostly watermark shade.

To unhide them, right click and select properties under General tab - attributes section at the bottom, deselect the hidden checkmark.

Disk cleanup:

First empty your wastebasket:
Right click on your Recycle Bin/Wastebasket on your desktop and Empty recycle bin/Wastebasket.

Next you can run MS Disk Cleanup Utility:
Double click My Computer. Right click on a Hard Disk, select Properties.

On the General tab, select Disk Cleanup to run the MS utility.

Temp files, 0 file size files, temp internet files are all usually safe to delete

Good Luck.

P.S. If you have Norton, when you empty your Recycle Bin, also delete Norton protected files. (That always seems too be holding onto some large unneeded files on my machine)