I did a fresh installation of Vista a few months ago, but from what I've seen, it doesn't completely "freshen" up my entire hard drive. What I mean is there are several items under my C: drive listed, and I have no idea what they are. And as I've stated in a previous post, it says I have a lot more space taken up than I really do.

What I really want to know is if there's a way to completely rid my hard drive of everything, (have all my original 150gb back) and then install windows from scratch.

And I apologize if I sound extremely needy in all of my posts, but I'm just completely clueless as to what to do, especially considering the poor performance of my computer that I have invested quite a bit of money into.

If you've got a floppy disk drive then write a windows 98 boot disk from this site: Bootdisk.Com
Restart your computer and set it to boot from the floppy once the command prompt comes up type in FDISK, hit "Delete Partition" and then "Delete Primary Non DOS Partition" or something like that, it should delete your partitions, when you reinstall Vista it should prompt you to format the drive, after all that it shouldn't report those files anymore

But after I delete the partition, that means I no longer have an operating system anymore, right? So would it still be possible to boot from my Vista disc in order to install it?

To be clear, this is an Operating System disc and not a restore disc, as in when you install Vista it's off the disc, if that's the case then yes.
If it's a restore disc that you got with a name brand PC then no...probably not

Yep-- you need ( in 98% of cases) a full-retail version of the Operating System-- or at least a full Version OEM disc-- NOT one of those @#$%%!! "restore discs".
Restore Discs make great coasters for your Beer of choice.

lol