Where are Compress Old Files on WinXP 32?

Just to satisfy my curiosity and make sure everything is in good working order in my machine. I would like to know exactly where these "compress old files" Are? I would like to find them Manually.

I tried using Disc Clean-up and it didnt remove the "old Files". So I set the days on how long it should wait to compress them from 25 to 150 days. Doing it that way, I was able to use Disc Clean-up to remove the "old Files". But theres still 255kb left. Its a big deal to me, even if its that small.

I've been trying to resolve this issue on my own on and off for about a year and I need some help.