Deletion isn't really a good first option (you have none left), 'first do no harm' don't delete, send virus to the chest and investigate. So effectively that is what you are doing when you delete shortly after sending to the chest.
There is no rush to delete anything from the chest, a protected area where it can do no harm. Anything that you send to the chest you should leave there for a few weeks. If after that time you have suffered no adverse effects from moving these to the chest, scan them again (inside the chest) and if they are still detected as viruses, delete them.
svchost.exe is the file name for an important system, a common tactic for malware to confuse users.
Where were these found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (C:\Program Files\Alwil Software\Avast4\ashLogV.exe), Warning section, this contains information on all avast detections.
Sorry I don't use MSN so I can't say and I have no idea what 'acting up' means, nor I would imagine would others who do use it, so please try to be a little more detailed.
