You're missing nearly everything. A full install is somewhere in the region of 15gb!
I've done some quick research for you. There are two possibilities. One is that the registry key that is referencing FSX is corrupt. You mentioned installing SP1? It is quite possible that it may have read and corrupted you registry key.
The other possibility is your Windows Installer is screwed. I would reinstall it first to eliminate it from the equation. Go here to download the latest redistributable http://www.microsoft.com/downloads/deta ... layLang=en
Once you have installed that, try to re-install/repair FSX first. If you try to uninstall it may not work as the installation is so corrupt. If this works and FSX installs, uninstall it all, restart, open up the FSX folder location and delete any left over folders and reinstall FSX. This will ensure that you can fully and properly uninstall FSX to give you a clean slate to work with.
If installing the Windows Installer doesn't work, and you are comfortable with using the registry, you can try this.
On XP hit Start > Run and type Regedit and hit OK
On Vista hit Start and in the search box type Regedit and hit Enter
Now you should have regedit open. Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft Games\Flight Simulator\10.0
Highlight the 10.0 folder and on the right pane a list of keys should be displayed. Check the CDPath key value points to your CD/DVD drive. For example mine is F:\. If yours is incorrect, double click CDPath and change the value to reflect the CD/DVD drive. If you have multiple, point it to the drive you have loaded the FSX DVD into.
Next is SetupPath, and this should display the location of the FSX main folder. By default it is "C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\"
If you left it on default during the installation, it should say that. If you changed the path that FSX installed too make sure it is correct in that key. If it is incorrect, double click the SetupPath and change the value to relfect the loaction of your FSX folder.
Once you have checked/changed this give the reinstall a go and follow the process above.