That one is actually in the FAQ :)

Check www.sharepointserver.com/faq.html

Thanks... I´ll read the information.

go to c:\program files\sharepoint portal server\bin or wherever SPS is
installed

in a command  prompt window
wscript msdmback.vbs /b <path for the backup  file>

In the Sharepoint help it says, "... nor can you back up individual
workspaces or documents."
Does this mean the portal I build does not get backed up? Only the
server? If the server crashes I have to start from scratch to rebuild
the portal?

No, it means that you can only backup  all the workspaces, document and
everything at once. If you need to restore a specific document, you will
need to restore the entire workspace and extract the document.

Everything in the workspace is being backup and can be restored, this
included dashboard, users, document, files  and others.

How would I go about adding a switch in my backup  line so that I
do not get the message box come up which prompts me to hit OK, when trying
to run  a backup?

This is from memory but you would add the //B switch that suppresses the pop
ups, but it also suppresses the error pop ups.

I have have scheduled every night, using the Win2000 task scheduler, the
backup of my Sharepoint server with this command  line in a .Bat File

c:\winnt\system32\cscript "c:\Archivos de Programa\sharepoint portal
server\bin\msdmback.vbs" /b c:\contenidos\backup.bak"

EXAMPLE:

echo off
for /f "tokens=2-4 delims=/ " %%a in ('date /t') do (set date2=%%a-%%b-%%c)
for /f "tokens=1-2 delims=:. " %%a in ('time /t') do (set time2=%%au%%b)

d:
cd backup
ren *.bak *.001

cscript "\\prove1dis1\d$\program files\sharepoint portal
server\bin\msdmback.vbs" /b
\\prove1dis1\d$\backup\backup%date2%-%time2%.bak"