I have just installed FC4 on an Acer 1690 notebook, and have just done some tweaking on xorg.conf to try to get my resolution to display at the proper resolution 1280x800. I am doing this using a program called 915resolution, and the program needs to be run before the x server starts. I would like to put this in a bootscript, but don't know how to create a bootscript in FC4. Thank you for your help!

You could have simply tweaked your resolution manually in /etc/X11/xorg.conf or using system-gonfig-display. There is no need to use a 3rd party app especially one that has to run at bootup.

I've tried that, it doesn't work. My xorg.conf is configured for 1280x800 right now, but it's simply not supported.

I know it's in /etc/init.d/, but I don't know what file to modify, or if I should create a new one...

From 915resolution's website:

915resolution is a tool to modify the video BIOS of the 800 and 900 series Intel graphics chipsets. This includes the 845G, 855G, and 865G chipsets, as well as 915G, 915GM, and 945G chipsets. This modification is neccessary to allow the display of certain graphics resolutions for an Xorg or XFree86 graphics server.

915resolution's modifications of the BIOS are transient. There is no risk of permanent modification of the BIOS. This also means that 915resolution must be run every time the computer boots inorder for it's changes to take effect.

I had a simular problem, but I managed to get it working like this:

(be sure to make a backup of xorg.conf, just in case)
In xorg.conf, delete the line that says: "Load DRI"
Than add your resolution at the appropriate place.
Reboot, or restart X
Done.

No need for third party apps.

Somewhere out there is web page explaining this problem (that's where I got this info) but I forgot to add it to my bookmarks and now I can't find it anymore

I'm not sure if Fedora differs much from RH8.

What is started at boottime, depends on the runlevel. In RH8, the gui is started if the runlevel in /etc/inittab is set to 5.
There is an associated directory /etc/rc5.d (similar for runlevel 3, there's a directory /etc/rc3.d).

In that directory you will find files starting with S and with K. Those are symbolic links to scripts in /etc/init.d. Anything with a K will be killed when the runlevel is entered, anything with an S will be started.
The programs will be killed/started in alpha-numerical order, so S99webmin will be started after S98wine.

The official way to start something is to create a script in /etc/init.d that starts the required program with its parameters and create the symbolic link Snnname in the runlevel at which you want it to be started. If it's just a simple thing without parameters, you can create a symlink to the program directly (this should work, but I've never used it).
I think (but I'm not sure) that x is only started after all other stuff in rc5.d is done, so a link called S99setup915 can be used.