Hi rmrg,
No, this Blaster virus (packed or unpacked) does not do any permanent harm... It just forces the computer to reboot on some systems (when RPC fails) and on 16th August and later floods one of the Microsoft servers with data (DDoS) - see the more detailed description on our pages.
To remove it, you can use our avast! cleaner (or just delete the msblast.exe file and the registry key) but as was said above - do not forget to apply the latest system patches!!!