When a program crashes, it will sometimes "dump" some or all of the
contents of RAM to a file on your hard disk. The file is only useful to
a technical support person who is trying to understand why the program
crashed. (Most tech support people have no clue what to do with a dump
Unless you've been asked to submit a dump file for inspection, feel free
to get rid of them.
Setup log files are files that "log" a program's installation. If you
look at one (they're really just text files - open with Notepad) you'll
see that they give a blow-by-blow description of how the program was
installed, in glorious detail.
If a program did not install properly, the setup log will tell you what
went wrong. If you haven't had an install go badly, feel free to ditch
these files as well.
On the question of how much free disk space is enough...there are no
standards. 15% of your disk needs to be unoccupied in order for Windows
built-in defragmenter to work. Beyond that, it's up to you.
Your CPU is another story. It won't be easy to find effective security
software that will operate on a P3. Even if you only use the computer
for basic items, an internet connection is basic enough for an online
criminal to find you.
Errare humanum est