I am still using 4.8 there is no big rush to go to 5 since 4.8 will be supported for quite some time, I personally like to wait a while and let them iron out all the bugs, let the ones that rush in find out all the problems, before I update. There have been several significant bugs popping up that they are working on and fixing. Some may have no problem at all where as some might never know since every system is different. I posted about some of them on the AVAST5 thread here. So that decision is totally up to you. You can put 5 over 4.8 as part of it's install process it will remove the old version however many people prefer doing a removal first, you will get both answers on this one.

you can not schedule a scan with Avast like you do some other programs, but the easy way to have it scan is to set the screen saver scan, anytime the screen saver is on the scan starts, it stops when you move the mouse then restarts where it left off when the screen saver starts again, that is how I use mine, if you go to the Avast site there are 2 pdf guides that you should read on how to use Avast and set up your scans and also to choose to do the boot scan or not. Adobe Acrobat (PDF) Document How to Install, Configure, and Use Avast Antivirus an excellent guide that answers most questions. It is not a good idea to keep your pc turned off and disconnected from the internet, when you get on it and connect you then are way behind in updates not only for your antivirus but for windows.

I sometimes speak up concerning others' suggestions that seem like Chicken Little-type fear mongering. I also think too many people have too many unsupported fears of unlikely risks on the internet and from PC use in general. I'm generally in agreement with Kudzu's comments, but let's be realistic - no one knows what the evil doers will do. Using an XP PC on a network that's unconnected to the internet - I'd say zero risk. Use it in full confidence until the hardware dies. Using an XP PC on the internet? Time will tell. Having capable firewalls, updated security software, etc., is a must for all PCs with all operating systems anyway. I have an XP PC that I use very occasionally that has all the protection reasonably available. I'll be sure to remove any personal info and will use it carefully. If I see any hint of odd activity, I'll just replace it. For most PCs old enough to have XP, spending good money to put a newer Windows on old hardware seems a poor choice to me.

Logfile of Trend Micro HijackThis v2.0.4 Scan saved at 4:47:37 PM, on 9/18/2011 Platform: Windows XP SP3 (WinNT 5.01.2600) MSIE: Internet Explorer v8.00 (8.00.6001.18702) Boot mode: Normal Running processes: C:\WINDOWS\System32\smss.exe C:\WINDOWS\system32\winlogon.exe C:\WINDOWS\system32\services.exe C:\WINDOWS\system32\lsass.exe C:\WINDOWS\system32\svchost.exe C:\WINDOWS\System32\svchost.exe C:\WINDOWS\system32\svchost.exe C:\WINDOWS\system32\ZoneLabs\vsmon.exe C:\WINDOWS\Explorer.EXE C:\Program Files\AVAST Software\Avast\AvastSvc.exe C:\WINDOWS\RTHDCPL.EXE C:\WINDOWS\system32\spoolsv.exe C:\Program Files\Zone Labs\ZoneAlarm\zlclient.exe C:\Program Files\AVAST Software\Avast\avastUI.exe C:\WINDOWS\system32\ctfmon.exe C:\PROGRA~1\Webshots\Webshots.scr C:\Program Files\Logitech\MouseWare\system\em_exec.exe C:\Program Files\AGI\core\4.0\AGCoreService.exe C:\Program Files\Java\jre6\bin\jqs.exe C:\Program Files\Common Files\LightScribe\LSSrvc.exe C:\WINDOWS\system32\nvsvc32.exe C:\WINDOWS\system32\svchost.exe C:\WINDOWS\system32\SearchIndexer.exe C:\WINDOWS\system32\SearchProtocolHost.exe C:\Program Files\Trend Micro\HiJackThis\HiJackThis.exe R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://go.microsoft.com/fwlink/?LinkId=69157 R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://go.microsoft.com/fwlink/?LinkId=54896 R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft.com/fwlink/?LinkId=54896 R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://go.microsoft.com/fwlink/?LinkId=69157 R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Window Title = Windows Internet Explorer provided by Comcast O2 - BHO: Adobe PDF Reader Link Helper - (06849E9F-C8D7-4D59-B87D-784B7D6BE0B3) - C:\Program Files\Common Files\Adobe\Acrobat\ActiveX\AcroIEHelper.dll O2 - BHO: Groove GFS Browser Helper - (72853161-30C5-4D22-B7F9-0BBC1D38A37E) - C:\Program Files\Microsoft Office\Office12\GrooveShellExtensions.dll O2 - BHO: avast! WebRep - (8E5E2654-AD2D-48bf-AC2D-D17F00898D06) - C:\Program Files\AVAST Software\Avast\aswWebRepIE.dll O2 - BHO: Java(tm) Plug-In 2 SSV Helper - (DBC80044-A445-435b-BC74-9C25C1C588A9) - C:\Program Files\Java\jre6\bin\jp2ssv.dll O2 - BHO: JQSIEStartDetectorImpl - (E7E6F031-17CE-4C07-BC86-EABFE594F69C) - C:\Program Files\Java\jre6\lib\deploy\jqs\ie\jqs_plugin.dll O3 - Toolbar: avast! WebRep - (8E5E2654-AD2D-48bf-AC2D-D17F00898D06) - C:\Program Files\AVAST Software\Avast\aswWebRepIE.dll O4 - HKLM\..\Run: [RTHDCPL] RTHDCPL.EXE O4 - HKLM\..\Run: [Logitech Utility] Logi_MwX.Exe O4 - HKLM\..\Run: [ZoneAlarm Client] "C:\Program Files\Zone Labs\ZoneAlarm\zlclient.exe" O4 - HKLM\..\Run: [avast] "C:\Program Files\AVAST Software\Avast\avastUI.exe" /nogui O4 - HKLM\..\Run: [NvCplDaemon] RUNDLL32.EXE C:\WINDOWS\system32\NvCpl.dll,NvStartup O4 - HKCU\..\Run: [ctfmon.exe] C:\WINDOWS\system32\ctfmon.exe ...