I was installing FC6 32-bit on a Toshiba Satellite A70, using GRUB to make dual boot WinXP or Linux. I remember a option to manage delay time, let default one OS, etc.
How to do by using the KDE/Gnome or console methods.

You can use any text editor you prefer, either graphical or non-graphical. You need to have root privileges to edit the file we're dealing with (menu.lst), so for example you could open it with kate as follows:
or, if you've configured sudo for your user, prefer to use this:
The file should be quite easy to understand and is probably commented so it explains itself. For example to set the time (in seconds) before booting the default choice, set timeout value:
would wait 5 seconds before booting.
To set the default OS to load, use default:
would boot the fourth menu entry by default (1st menu entry is number 0 [zero]). The rest of the file should be easy to understand..

NOTE: if you set the default to some numeric value and update the kernel, it's possible that the newly added kernel "messes up" the default value so that it's wrong by one; some distribution(s) are "clever" enough to set the default value to the entry you want it to be, but most will just add the new kernel in the list, thus making the list longer, and because the new kernel is added to the beginning of the list, your default value becomes one too big (i.e. if the default was '3', it would boot fourth entry by default, but when a new kernel was added to the beginning of the list, that number was still '3' but now it pointed to the new fourth entry and not the one that was fourth before the list update). So after doing a kernel upgrade make sure your menu.lst's default value is in order