> I have installed unixodbc and rubyodbc . I try to test the 
> connection to my
> sql7 server
> 
> The syntax is  :  ruby test.rb DSN [uid] [pwd]
> but what is exactly DSN ?

DataSource Name. If you're on Windows NT, open Control Panel, ODBC Data
Sources (w2k it's under Administrative Tools). You can set one up in there. 
 
However, I usually don't use DSNs, plus I assume you're on unix, which I
have no idea if it supports dsns (contact the Ruby/ODBC author, he might
know), so you can go a more direct route with drvconnect:
 
def getDB(server, database, user, password)
  drv = ODBC::Driver.new
  drv.name = "SQL Server"
  drv.attrs["server"] = server
  drv.attrs["database"] = database
  drv.attrs["uid"] = user
  drv.attrs["pwd"] = password
  drv.attrs["driver"] = "SQL Server"
  db = ODBC::Database.new
  db.drvconnect(drv)
  db
end

The attribute values for the connection string will vary from driver to
driver, but the above works for SQL 7.

Chris