Whenever my Windows rubyw script launches a subprocess, a command window 
pops up and immediately disappears.  How can I keep this from happening?

Details:

I keep a daily log of what I do at work.  At the command line, I type 
"log" to edit the current day's log file.  A Ruby script generates an 
appropriate name for the file automatically, then launches vim.

Now I'm trying to use the Windows GUI, and I want to have an icon I can 
click to launch gvim.  Here's the code:

   # log.rbw
   # Launch gvim on today's logfile, e.g. on
   # C:\Logs\2006\2006.01\2006.01.26.txt

   logfile = Time.now.strftime('C:\Logs\%Y\%Y.%m\%Y.%m.%d.txt')
   system("gvim", logfile)

When I click the icon, I get the expected behavior, except that a 
Windows cmd.exe window flashes on the screen first.  :(