does rsync run as a service?

[dtra]

hi all

sorry for the question, but i can't seem to find information on this
i'm a linux novice, we are looking to do web server backups
i'm using redhat 9, rsync 2.6.4 (among others, rhel3 as well)
but is rsync always checking for changes
or does it only run when invoked from the command line (if this is the 
case, can it be run as a service, and would this be practical if there 
are constant file uploads)?

one more quick question, do different versions of rsync work together?

thanks
dave