1. is this message at the boot screen(black background, white letters)? if so it is saying there is no drive attached to the primary IDE channel so the OS must be installed on a Sata drive. or IDE drives are not jumpered correctly.
2. themes can be found around the net like http://www.softpedia.com/progDownload/Roya...load-13027.html
the royale theme is there. themes would also be on the install cd and it would take some legwork to find out which .cab file they are in and how to extract them to the folder where windows keeps its themes, but it can be done.
3. its possible that your video card does not support that resolution. see if there are new drivers for your vid card and if you haven't already, install the drivers for your monitor.
4. i have no idea why windows installer would just pop up unless one of your programs may be trying to update. you have to be careful of rouge programs (i.e. trojans) trying to install. next time it happens i would unplug from the internet and see what it is trying to install. keep virus scanner up to date and turned on.
5. bleep, i wish i read number 7 first. two (or is it three?)antivirus programs running at the same time can cause lots of problems. uninstall pc tools anitvirus and firewall, out-dated norton anitvirus, threatfire and reinstall the one you like. AVG and Avira make good free anti-virus programs. hijackthis can be uninstalled. you can reinstall if and when you need it. sybot which i hope is spybot is a very good program i would keep as is atf-cleaner.