Yes, but you should turn off appending tag messages to incoming email in the NOD32 IMON setup, or set IMON to append it to infected email only.

Could I use AVG Anti-Virus Personal E-mail Scanner and GetByMail at the same time?

No, GetByMail is not compatible with AVG Anti-Virus Personal E-mail Scanner. Disable AVG Personal E-mail Scanner plugin before running GetByMail or use any other free or commercial antivirus software: avast! (is a free full-featured antivirus package), AntiVir, Sophos, F-Prot, Norton AntiVirus, etc.

Could I use my e-mail client program and GetByMail at the same time?

It is strongly recommended to shut down your e-mail client program (Microsoft Outlook Express, Mozilla Thunderbird, The Bat, Eudora...) to assure reliable work of GetByMail. In other case you should configure your e-mail client not to remove messages from the POP3 server. Microsoft Outlook Express users can change the setting to "leave a copy of messages on server" under Tools->Accounts-> [Select Account] ->Advanced tab->Delivery section.

In any case it is not recommended to read/send messages during GetByMail work.

Does GetByMail support Google's GMail?

GetByMail supports SSL connections over POP3/SMTP or IMAP/SMTP protocols and is compatible with Google's GMail service. See Local Mail Configuration for more details.