Can you boot from a Linux CD? Maybe you can manage the files from it.
To know if a file is a false positive, please submit it to VirusTotal and let us know the result. If it is indeed a false positive, send it in a password protected zip to virus@avast.com
Please, mention in the body of the message why you think it is a false positive and the password used. Thanks.
Other possibility is JOTTI. VirusTotal and Jotti both have file size limits 10 and 15MB each.
I suggest also a full computer on-line scanning:
Kaspersky (very good detection rates)
ESET NOD32
Trendmicro housecall
AVGas (does not necessary if you have AVG antispyware installed)
F-Secure
BitDefender (free removal of the malware)