anyone no a version of Avast support for Ubuntu AMD64-bit?
Jetson53 
From what i seen there is no support for it.
Operating Systems Supported
Windows 7 (any Edition, 32-bit or 64-bit)
Windows Vista (any Edition excl. Starter Edition, 32-bit or 64-bit)
Windows XP Service Pack 2 or higher (any Edition, 32-bit or 64-bit)
Microsoft Windows 2000 Professional Service Pack 4
I don’t believe Avast support Ubuntu OS if I’m not mistaken ???
There is linux version which does support ubuntu: http://www.avast.com/linux-home-edition Haven’t you seen that there is a linux sub forum: http://forum.avast.com/index.php?board=5.0 speedy? 
The system requirements you have posted is of the windows version. Here is the one for linux version: http://www.avast.com/linux-home-edition#tab3
And as you can see here: http://www.avast.com/linux-home-edition#tab3 it doesn’t support 64 bit OS.
jetson53
Try this page.—> http://www.avast.com/linux-home-edition#tab4
Once you download the .DEB file you will need to install it using Terminal and tell Ubuntu to force architecture.
For Example:
sudo dpkg -i --force-architecture avast4workstation_1.3.0-2_i386.deb
I installed Avast for linux on ubuntu 64 once and it worked just fine, I don’t remember if I had to install a 32bit library manually or if ubuntu install them for me automatically.
I personally use Mandriva and Mageia (Mandriva’s Fork) in 64 bit, and the only library I had to manually install was libexpat0-1.95.8-4mdv2007.1.i586.rpm, and that’s because Avast hasn’t been updated in a while to support the latest libexpat1.
Best Wishes,
I did a search on the avast web forum… and found something but idk if this will help or not but http://forum.avast.com/index.php?topic=79220.msg653529#msg653529 is what i found 