Good virtual machine setups for card farming?

idlemaster will give you sporadic card drops.

I second idlemaster.

https://nodejs.org/ with this i think you can farm cards even without installing steam, you could even run it on a raspberry pi or arduino so you can save energy :p

have myself a few in Oracle VM Virtual Box for various purposes > 3x Win7, 1x XP, 1 Win8
all would work for farming but as mentioned above far easier getting: http://www.steamidlemaster.com/

and if you want to run 2 idlemaster without a Virutal PC - run a sandboxed version of steam here a guide:
http://steamcommunity.com/sharedfiles/filedetails/?id=311943358&insideModal=1

(+ if you had a liscensed version of sandboxie you could run as many steam accounts
and idle master's sandboxed as your RAM allows with free ver. only 1 sandbox at a time)

I use custom nodejs script to idle all alts (works fine idling tens of accounts).
Another program for registering keys & sending trade offers with ease.

Keep in mind that you can run games simultaneously for the first 2 hours, and after that one by one for the drops.

I'm currently trying out Idlemaster on an alt account, if this really works than it's a huge time/effort saver.

Sorry, I know nothing about farming, I have no interest in cattle and fertilizers.