clarification for you. Forgive me if it seems I'm telling what you already know as "I don't know...what you don't know".
Service packs are collections of security & performance fixes. MS usually issues fixes monthly & when enough are out they bundle them together as a SP (SP2/SP3) for each OS.
One thing about SP's is that they require your machine to be COMPLETELY clean of Spyware/Adware/Trojans/Viruses/etc. BEFORE you attempt to install them. Otherwise you end w/ a he.. of a mess & possibly non functioning machine. They also usually require legit OS and previous SP's to be onboard. IE: SP2 installed before installing SP3. Older versions of QT may agree with your current machine but likely won't be able to handle/show newest QT file types such as course likely uses.
It sounds as if newer Quicktime program, requires SP2 to be installed at minimum as it uses the SP2 changed routings to function. If you could get it to install, it would be trashed & the bugs would likely make machine unusable.
If you delete the Quicktime Icon from your desktop,you delete ONLY the Icon itself (the path to the program from desktop).Does NOT delete/un-install program itself. This is usually done via Control Panel>Add/Delete programs Icon>clicking to highlight & clicking remove.Followed by a reboot. Often a good idea to create a restore point before doing this (just in case).
Often, if you check the Start>All Programs list & put cursor over the program name, you'll get a drop down list & often there is an Un-install option there you could also use. If it is the same version you tried 2 times, the un-install (IF there at all, since install didn't complete)should remove "both".
As a self described modest newbie, I suggest that REQUIRED malware clean-up & subsequent installs of SP's & possibly updated drivers
(assorted) needed for computability w/ newer SP (which must be downloaded & saved OFF machine(Floppy/CD/DVD/USB flash thumb drive) BEFORE installing SP2 etc. IS NOT, repeat NOT, something you should try alone. At least a friendly Nerd or a professional to help or do it for you will be required. Sorry!!
Possibly, easiest answer (if you can find one now) would be to buy a legit retail XP disk w/ SP2 included & do a complete new install from a blank page (so to speak). Even this will require getting in Advance (OFF machine) such assorted drivers for your motherboard/Audio/Video
cards that are updated for SP2. Ones included in XP are VERY basic & minimal & not suitable for much beyond booting up. Possibly a somewhat used XP SP2 machine from somewhere like Factory Direct with legit XP already installed & at least w/ some warranty might be another option
in the $200-$350 range. I usually don't suggest this but if necessary....probably only a little more than retail OS alone.
At least this will by-pass any problems of existing malware/spyware currently in your machine.
I DO NOT recommend VISTA (any) for your current specs without some major hardware upgrades at which point buying a new machine ($500-$700) would probably be cheaper & at least you'd have a warranty rather than a 5 year old HD etc. possibly ready to die soon.
Again, my sympathies for this news. If you get a new machine, you could keep old one for mundane tasks like mail,playing /Videos/Music
more basic games etc. Depending on your current printers etc, some of those may not work w/ post SP2 machine (I had to get new printer & scanner since old not compatible ) but since they work w/ current, you could continue to use for those purposes. Good Luck!!!