how do I update to the most recent version of KMyMoney?
Update to the latest version of Ubuntu
When using an older version of Ubuntu, such as 10.04, the easiest way to get the latest software is to upgrade to the latest Ubuntu (currently 11.04). Updating Ubuntu will also update all of the software you have installed (if updates are available).
The version of Ubuntu that you're using is a Long Term Support release, so by default, you won't be prompted to upgrade. If you want to upgrade Ubuntu, go to System > Administration > Software Sources. Then, under the "Updates" tab, set "Release upgrade" to "Normal Releases", then run Update Manager and check for updates.
I have installed KMyMoney 1.0.4... but there is a more recent version available from the KMyMoney website (4.5.3)
The change in version number may look significant, but KMyMoney actually just updated its version number to match the rest of the KDE platform. Unless you know of specific features in the new version that you don't have in 1.0.4, I wouldn't bother with the update.
Add a PPA
If, for whatever reason, you'd prefer to stick with the Ubuntu 10.04, but you really want the newest version of KMyMoney, you'll want to add a PPA. When you add a PPA, application updates will be installed through Ubuntu's Update Manager. Keep in mind that these updates are coming from a third-party, and you should only add PPAs from trusted sources.
I'm not sure why the PPA didn't work for you before, but in theory, this would be the way to go. This is the PPA you want: ppa:claydoh/kmymoney2-kde4 See here for more information on how to add PPAs to Ubuntu 10.04.
what is the difference between the KDE desktop and the standard gnome desktop
KDE and Gnome are the two most popular desktop environments for Linux. Generally, the desktop environment controls the look and feel of the user interface and the default applications (web browser, text editors, email client, etc). You can find a lot about the specific differences on Wikipedia.
if I install KDE4, how do I select one or the other at boot?
On the login screen you'll be able to choose which session (Gnome or KDE) you want to use.
Can I run KMyMoney in gnome (do I need KDE)?
You can run KMyMoney in Gnome (this is what I do), but if I remember correctly, it depends on a lot of KDE libraries and tools, so it will install a lot of extra stuff. This shouldn't be a problem unless you're really low on hard drive space.
Anyway, welcome to Ubuntu, and sorry it took awhile for your question to get answered. If you have any other questions, don't hesitate to ask.