Web site failover

[Ned Trilby]

How can I set up a failover (within 4 hours) of a website? My site
"TEST111.com" is running in "SITEA" with ISPA as the ISP. If SITEA
burns down I have a standby machine in SITEC with a connection to
ISPB. Can ISPB take over traffic for "TEST111.com"? How is this
achieved? I would only see my standby machine connected to the
Internet if the original machine in SITEA fails.
TIA,
Ned