I'm basically an ordinary web user and I've managed to install all sorts of CMS's: drupal, mambo, pmachine, expression engine, plus various forums and galleries. Here are some things that I see or do over and over again to install these packages that I wasn't born knowing :-) My suggestion is to google the key terms to learn about them, and read instructions that mention them in context.
1. Learn to log in to your shell account. You can do many or even most things necessary to install a CMS using a good FTP client, but it is helpful to know what the FTP client is doing 'underneath the covers.' I also find that working in the shell is often a lot faster.
2. Learn a few basic UNIX or Linux commands to do things like make a directory (mkdir), list files (ls or ls -a), change directory (cd), rename a file or directory (mv). If you are logged in to your shell, you can usually type 'man cd' to read help information about cd or most other commands. Or just google.
3. Learn how to change file and directory permissions. Almost every install requires you to set various permissions to various settings. You might use an ftp client to do this, or you might do it in the shell, using the 'chmod' command.
4. Learn how to unpack an archive using 'tar'. You'll also want to learn how to make an archive using tar, as it will allow you to make backups of entire directories with ease. Many CMS's come packaged as 'tarballs' and will need to be unpacked into the final directory structure. There are also programs that do the unpacking (Stuffit, WinZip etc) or you can do it on the command line in your shell account.
5. Learn to use a text editor and open, edit, save, and close .php files without damaging them :-) You will often have to open a file named something like config.php and change some values, usually to list the name of your mysql database, the 'username' of the database, the password for the database, and the name of the web host of the database.
Dreamhost will let you choose PHP4 or PHP5 for any given domain, so as you read the system requirements for stuff, if it says 'only works in PHP5' or whatever, don't worry. You'll probably be able to run it.
Your web panel will lead you through the process of creating an empty database. As mentioned up-topic, MOST installers will automatically populate the database. The key things I suspect are behind some database installation frustrations are these:
1. The database must have a 'hostname' and at Dreamhost your database is NEVER 'localhost' - you will ALWAYS need to specify some name like 'your-database.yourdoman.com'. Almost every application will ask you for these things, all of which are set up by the DH panel: username, password, hostname, database name. The username and password are special to the database and not your regular login. Again, the panel will lead you through it.
2. WAIT for the hostname to propagate. Sometimes they seem to go 'live' in minutes, other times it takes until tomorrow! I usually check by clicking on the database on my web panel. When the empty database finally loads up without error in phpMyAdmin (the database tool thingy) I know I can reach the database and it's probably safe to start installing my application.
I don't know if this gets anywhere near the kind of things you are looking for. Apologies if too simple.