The Microsoft Security at Home group has published a list of Windows Vista Beta 2 Antivirus Partners:
Although Windows Vista is still in beta, we realize that many customers are testing it in production environments. Microsoft has been working closely with our antivirus partners to ensure that Windows Vista Beta 2 has the same antivirus protection as previous Windows versions.
As an aside, I should point out the absurdity in that last sentence: Previous Windows versions have no antivirus protection, and neither does Windows Vista. Ahem.
Anyway, I previously mentioned the one-year free subscription to CA’s eTrust EZ Antivirus. This page now also lists a free trial of Trend Micro’s PC-Cillin 14.55, good through October 31, 2006.
Ed Bott 
I seem to remember that DOS 6.x contained a small anti-virus program. And course DOS was the kernel for Windows 3.x
You have a good memory.
MS-DOS 6 had Microsoft Anti-Virus, which was written by Central Point Software. If you installed Windows 3.11 over it, you got Microsoft AV for Windows. It was never updated.