The term Data Guard came along with Oracle version 9 ( completely obsolete too ). In Oracle 8 it was called "Standby database".
You should upgrade to at least Oracle 11 and then consider using Data Guard. Trying to use Oracle 8 will give you nothing but headaches and you will have learn a ton of things which are no longer true.
Yeah its too old era, There are changes from version to version and release to release..
As said by mseberg Data Guard there is no concept in 8i where it is called simple standby database and you cannot avail high availability features with this version of course still you can manage standby with manual recovery. But lot of manual tasks has to be performed such as copying archive files, recovery stop and start so on.
So very very limited in terms of high availability instead of that you can say alternate database which is available to you in case of primary is unavailable.