Vista includes all Version on a single DVD. The are all saved as several images in a huge container file (install.wim). Because they are independent you have to select a special version and apply the updates for every version again.
first you must have Sp1 installed, now apply the registry settings and search for Updates. Now install the servicing Stack update and reboot. Now search for updates again. If the Sp2 isn't shown, reboot and try it again until it works
Vista doesn't include .net 1.1 and older Dx9 versions, only Dx9c (core dlls). If you need the managed Dx DLLs you have to install the latest Dx Runtime
How do you start your application? if UAC is on, you're not elevated rights by default. So tell your application it should run with elevated rights (this can be requested by editing your manifest file)
hmm, I've never uninstalled the fix. Try the same thing in a Virtual Machine: Install your Vista, install the updates and remove KB955020. Now check if your issue happens again.
but only if you disable Superpetch yeah, this is a must have. You should always use superfetch and superfetch isn't the cause for your occasional disk activity