Hello Zyndstoff!
Here is an extract from the avast support webpage:
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=750&nav=0,1#idt_01"What are the supported operating systems for avast! 6.x ?
The supported operating systems for avast! Internet Security 6.x are Microsoft Windows XP Service Pack 2 or higher (any Edition, 32-bit or 64-bit), Microsoft Windows Vista (any Edition, 32-bit or 64-bit) or Microsoft Windows 7 (any Edition, 32-bit or 64-bit).
The supported operating systems for avast! Pro Antivirus 6.x and avast! Free Antivirus 6.x are Microsoft Windows 2000 Professional Service Pack 4, Microsoft Windows XP Service Pack 2 or higher (any Edition, 32-bit or 64-bit), Microsoft Windows Vista (any Edition, 32-bit or 64-bit) or Microsoft Windows 7 (any Edition, 32-bit or 64-bit).
Note:
The above means that avast! 6.x isn't supported (isn't compatible, can't be installed and won't run) on DOS, Microsoft Windows 3.x, Microsoft Windows NT 3.x, Microsoft Windows NT 4.0, Microsoft Windows 95, Microsoft Windows 98, Microsoft Windows ME, Microsoft Windows Server operating systems, or any others which aren't specified as supported."
So in my opinion is that Windows 2000 IS SUPPORTED for avast! Free & Pro.
Regards!
INGBEAN