Well, since you've posted this in the VB section, I assume you're thinking about making it in VB. If that's the case, I wouldn't. There's actually a bunch of information on VBF about people who have tried to create a VB Antivirus app and have pretty much failed. VB is an awesome language, but not really suited for this type of thing.

C++ is probably the best language to create an AV app in.

For the database, most AV apps usually create their own, if I'm not mistaken.

You won't really find any sample code for it. But, Google rarely fails me