Is Win XP up to date? SP 3 installed, all updates done? 
It's my father's computer. He hasn't used this one in years. Which is why I'm doing the responsible thing and updating it for him, with the help of someone 6 time zones (and techie light years) ahead!!
I did download SP2 last night (rather, early this morning), and am now installing SP3, which is, by the way, 66.9MB, according to the info in "Review and Install Updates," and not 316MB. Perhaps they found a way to streamline it.
Oh my bad... I am stupid. 
Great that you managed it anyway, I wasn't aware that it's an ftp-link. I will try harder... 
YOU are not "stupid." It was me who acted "stupidly" by not double-checking and making 100% certain that Norton was not installed anywhere on the computer prior to installing Avast.
...these two programs interfered with each other by blocking the files for the respective other program - thus caught in between those two AVs the programs could not be executed and the errors resulted.
I surmised it might have had something to do with a conflict between the two programs, after discovering Norton was, in fact, installed on the system.
Never install more than 1 real time antivirus scanner at a time.
I know this. Really, I do.
As you so succinctly put it,
I will try harder.
A lot of updating work to do...
On it! Still installing SP3. ("Verifying the download.")
As far as browsers go, I also prefer FireFox, though it's perplexing that it still--constantly and continually--sucks up all available CPUs after it's been open a while, even though it's been updated many times over the past few years. That is it's biggest drawback, in my opinion.
Fortunately, Session Manager allows me to save my work, restart the program, and resume where I left off.
Will continue the update process, and return upon completion.
THANK YOU for your time and efforts on my behalf, Steven! So very much appreciated.
Kat
