I don't have Acceleration so I can't help you out specifically with the F18.
BUT, I've been using FS for years and also fly for real.
When changing the frequencies you don't need to worry about .
Personally I just use the mouse and change the frequencies that way.
LORAN I've never used, nor seen in FS but then I tend not to pay that much attention to it....
I'm guessing you are using the built-in flight planner? If you are then your GPS will automatically load that flight plan. If you are flying something a little more complicated with an FMS then usually there is an option in the FMS to load the FS Flight Plan.
Once you've checked the flight plan is in your FMS/GPS you need to make sure that the autopilot is looking at the GPS/FMS for its NAV instructions.
Usually you will find a switch that is marked NAV/GPS. You need to make sure this is set to GPS, and then with the autopilot on you select the NAV submode. While every autopilot is different there should be a NAV mode.
Now if you're using an FMS it can build you an altitude profile. But generally the altitude management is your problem if you are using GPS. You can set up the Garmin's to give you cues for vertical navigation. I'd suggest for that information you go to Garmin's website - www.garmin.com and download the GNS4xx training devices. The GNS in FS is very close to the real thing.
Now forgive me if I'm teaching you to suck eggs, but with the ILS I'll start from the beginning. We'll use the ILS at Southend Airport [EGMC].
We know the frequency for the ILS there is 111.35 and the Ident is I ND. We have also found out that the runway heading for the ILS is 237.
In you NAV radio you need to dial in 111.35 (again just use the nobs on the radio and a mousewheel to scroll through them. That's the easiest way and its the way it's done for real!). Make sure that it is the active frequency.
Now depending on which aircraft you are in... Depends on what instruments you have.
If you have only VOR receivers you need to turn the dial so it reads 237.
If you are flying something a little more modern you will probabyl find that on the autopilot panel next to the heading selector (or sometimes the same button) you'll see something to set your course.
Course needs to be 237.
Now in the real world you listen to the NAV frequency for the morse code ident, in this case we'd be listening for IND... If you can hear it, then you're picking it up.
That is all you should need to do to set up your aircraft to fly an ILS approach.
Don't forget that you either need to fly a procedure in, self-position or get vectors to the ILS.
If you are using the Garmin GPS on FSX you can use the Approaches in there. Just load up the approach interface and select an ILS24 approach for EGMC and then you'll get a couple of options for how you want to get there.
Ideally you want to be interceptiing the localiser (the vertical bar on the HSI/VOR/FD that gives you your position relative to the centreline) by no more than 30 degrees.
If you are going to use the autopilot to fly the ILS for you, generally it isn't switched to APR (approach) mode until you have intercepted the glideslope. Once you get the glideslop, you can let the autopilot fly the apporach if you so wish... Just hit the APR button, depends on the aircraft thought.
I can't take screenshots because my harddrive for Games went bang and I haven't replaced it yet.
But if you are still stuck and confused, PM me. And if possible include a screenshot/s of the cockpit you're using and I can highlight from there.