DOCBOOK: DocBook XML V4.1.2<==Will not Execute?

Good Afternoon

Recently downloaded your DocBook XML V4.1.2 as I want to learn more about
SGML/XML but
when I unarchived the files and clicked on Docbook.cat received a Box
message: "Invalid Public Key Security Object File"
and below another message "This is an invalid Security Catalog File". As I
stated, I'm new to XML and maybe my system requirements are not up to par or
I need some other software to run DocBook, if so, please advise.


CPU: AMD K6 300
128k ram
CDRW
SoundBlaster Live
ATI magnum xpert 128
Win98 1st edition (all security fixes and updates installed)
I.E 5.5



Thanks,
Mcasey