Open the terminal and type: su-
, then enter root password. Now issue command: gedit /etc/modprobe.conf
I'm assuming gedit is installed by default in Gnome desktop, running the gedit command as root will open the graphical editor as root so you can make the changes to the file and save it from the file menu.
I don't have Fedora 10, if it does not have gedit, you'll get a "command not found" error. If that happens, issue the same command using the name of a graphical editor you know you have instead of gedit.
There are some command line only editors like vim, but a little tougher to explain in less than 200 words. If the full version of vim is installed, issuing command: vimtutor
will put you in a half hour course on learning it.
When I did use Fedora, I found this guy's tuts
were very helpful.