I cannot install any new applications to a brand new N810. I have upgraded the system software to 2.2007.51-3, and I am connected wirelessly to the internet.
When I try to install any application with Installation Manager I get the message "Unable to install ______". I get this for Skype, Camera, radio, everything.
I have the Nokia catalog enabled.

Anyone got any suggestions before I throw this into the ocean and consider it a total loss?

try reflashing to the most recent version of 2008 instad of 2007. I don't think 2007 is meant to run on the N810.

2.2007.51-3 Is the name of the 2008 release oddly.
What does it say if you press details?

btw; do you have access to a linux machine?

Yes, version 2.2007.51-3 is what I have installed - which is indeed oddly named. When I try to install any of the applications the message I get is "Unable to install ______". If I attempt to install skype, for instance, then the message is Unable to install Skype. The message does not allow me to get any details. I can only close that message.
This happens if I either attempt to have the skype site install it, or if I download it and save it to memory and attempt to install from that file. Same error message.
Unfortunately I do not have access to a linux machine, only windows.

Copy the files in the internal memory somewhere, format the internal memory, and try again. You could have the read-only internal memory bug.

I think there is a general problem, not limited to the OP.

Try the Geneven Challenge to prove me wrong:

1. If you have Skype installed, uninstall it.

2. Then try to reinstall it.

3. Try the same with, say, Mauku.

I can't reinstall them when I try it.

I have the latest OS, the one referred to in this thread.

Ok, thanks.

It would be easier if you had access to a linux machine because then you could set R-D mode which would enable root access in the terminal, and then you could run "apt-get install camera" for example and we could see the output there.

Root mode may still be done but in a longer way. I'll leave it for now.

Nevertheless, when you get the error message, what does Tools > Log say?

Here's how I solved my problem, which was virtually identical to yours. It took about five minures.

I decided to focus on the Skype program. I found from the Gronmayer site what repository it was in. I went into Application Catalog and deleted all repositories except that one. I then allowed the registries to refresh. I could then install Skype.

First of all, thanks to all of you having suggestions. I'm at a loss without them.
When I try to install Skype, for instance, the tools/log says:

hildon-application-manager 2.0.
------
Installing Skype 1.7.62.51.1
Failed using a MMC to download packages, Using default
E: Can't create directory at /media/mmc2/.apt-archive-cache/: Read-only file
E: Unable to lock the download directory


I will try the other suggestions later today and will report back.

That sounds like the "read-only internal memory card" yerga mentioned. Try this simple test : open the file manager, copy any file from, say, your Documents folder, then move to somewhere in the "internal memory card" and try to paste it there. Does that work ?