I have installed Avast 5.0 over Avast 4.8 on my 2 computers, both XP and my mom's XP. All 3 installs went well and no problems. I didn't not uninstall 4.8 before hand. I did this a month ago. All three computers are having no problems.
Before install, I did make sure all 3 computers were free of spyware and defraged them if they needed it.
I just wanted to report my experience.
Thank you, Avast! My mom and I are very appreciative of all the work being done, by your team, to keep our computers safe.
Becky