I am very close to the same situation as far as using Avast free antivirus 6.0.1203 on a Compaq Presario SR1710NX with ONLY 256 RAM memory running Windows XP with service pack 3. Of course my situation is different in that I'm using service pack 3 instead of service pack 2.
I agree that it would be wise to go with service pack 3 as it is or will be very soon the only XP operating system that MS will support going forward for awhile. Also there are a lot of issues with service pack 2 that are resolved with service pack 3 which includes not just security but compatibility as well. I would that I would agree that with 256 MB ram it gets pretty darn slow when updates are running i.e. Avast for example, to the point that the computer very nearly comes to a stand still for some time. Because of this I ONLY have Avast that runs "automatic updates" along with PEN for email notification.
That said, I didn't see any appreciable increase in slowing down at these times with service pack 3 compared to service pack 2.
As far as the missing
volume control icon in the system tray is concerned. I've noticed that a couple of the icons WILL disappear from the system tray from time to time. They include the
volume control icon mentioned in this thread and in my case PEN email notifier as well. What will happen is they will disappear for a while and usually return, but sometimes will not.
I have improved on this situation by not having ANY system update programs running in background with the ONE exception of AVAST. So I've got "Windows Defender" on "manual" updates as well as "Automatic updates" in the "Security Center" (program updates) as well as "HPDJ Task bar utility" and "HP Software" updates etc. These are all a drag on the system and are utilities I can do manually at my convenience.
By keeping the start-up processes that would normally be running all the time at a minimum like I mentioned above all I have to deal with is when Avast updates which as I mentioned admittedly does really bring the system to a crawl. Other than that however, I have generally AVOIDED the "missing icons" issue in the system tray including the
volume control icon by limiting the update types of programs that start-up on boot-up thus this pretty much addresses the issue in this thread and the system runs reasonably fast considering the limited RAM as long as AVAST IS NOT UPDATING THE VIRUS DATA BASE THAT IS