i’m in Safe mode right now 
since i uninstalled Avast 4.8 my win XP wont start up!
today i’ll format my PC and install win XP-SP3
i wonder if i need to download Microsoft .Net framework b4 i install Avast v5?
If yes which version do i need for Avast or even for my PC?
I don’t believe you will find .net framework in the system requirements of avast5, that is what I would check first.