While remote in to Remote Desktop how can I press the fn key on the Dell keyboard using software only?

No, you need to connect the projector to your laptop and press Fn and F8 to load to the projector. Then you can open a remote desktop session and it will be displayed on the projector screen.

Hope this helps.
Karl

Just a shot in the dark, but have you thought of doing it programatically?  i.e. write a little program that you can run after you've logged into the remote session that will "stuff" the keyboard with the keys you want?  

Umm... I am not sure that I worded the question correctly.

1. I do not have physical access to the laptop.
2. I can get in with Remote Desktop.
3. Once in, How can I press the Fn and the F8 buttons using only my session, a soft keyboard, or some other type of software only key combo? ie... The ASCII key set?

Let me be sure that /I/ have a clear picture of the layout:

1.  You do not have phys. access to the laptop and the projector is attached to the laptop.
2.  You will be remote-ing into the laptop and once there you want to trigger the function+f8 key on the laptop so that it will activate the projector.

If this is the scenario, I would think that you could create a small program in VB or some other lang. that's handy, possibly even a .bat file, that pushes those keys into the keyboard buffer.  Just put a shortcut to the little program in the start menu of the laptop and when you need to activate the projector, just run the program.

In VB, for instance, the command would be:  sendkeys {"Fn"}+{F8}

The reason I put "Fn" in quotes is because I can't say what the key-equivalent would be since it's a non-standard key.  I'm not sure there would be a way to send that key.  Do you know if there is another way to activate the projector using an alternative key combo?

Here's a link that discusses how to find the scancode of Fn+key combinations:

http://tiny.cc/CQWSK 

According to this page:
http://www.haverford.edu/av/techdocs/laptopchart.html

The following keys are used on various Dell laptops to activate the projector port:
         FN + F8
         FN + F12
-->    Ctrl + Alt + <
         FN + D
-->    Ctrl + Alt + F10

If either of the combos that begin w/Ctrl work on your laptop, then the solution becomes much easier.

Another alternative you already mentioned:

Start->Programs->Accessories->Accessibility->OnScreen Keyboard

it /might/ have the Fn key on it already, if not, you might be able to wrangle a different version from Dell.

Just curious, did you ever get this working?

As someone who devoted quite a bit of energy and time to suggesting several possible solutions, I have an interest in the disposition.