I set up SL5.1 so that after boot I get the VGA console, log in there
and eventually do a 'startx' when GUI is needed.

The only problem is that 2 'X' processes are created instead of 1, as
reported by 'top':

  PID   USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  13908 root      15   0  138m  45m  14m S  1.3 10.4   0:14.86 X
  13914 root      21   0  138m  45m  14m S  0.0 10.4   0:00.00 X

Killing the one that never got any CPU time (but still seems to be
eating memory) shows no adverse effects, but why is it there in the
first place?

I am using the stock 'startx' script that came with SL5.1.

TIA for your comments,
Andrea