I see in the properties tab of the BOINC manager two different memory listings:
Virtual memory size
Working set size
What is the difference between the two? Is the virtual size the amount of RAM reserved by the task and working set size the amount actually used? Specifically, if I am in one of my micromanaging moods, is the virtual memory size the amount of RAM held if I were to suspend a task to run another and thus unavailable to BOINC or the system as a whole?

Tell you what it is: 'Virtual' memory is the not-real, memory extension on the storage device, usually the hard-disk. This is where the overflow goes when RAM availability is short. Also called Swap or Paging-File, it's much slower.

Unfortunately I have no BOINC with a 'Properties' tab, it does though have Disk & Memory in the computing preferences screen. When you set Ram [memory] too tight, more swapping to virtual memory happens, to the point you could get disk-trashing because tasks are constantly storing and fetching parts of a job from the drive. Partly though BOINC will stop 1 or more jobs if there is not enough 'Working' memory accessible.

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Coelum Non Animum Mutant, Qui Trans Mare Currunt

Unfortunately I have no BOINC with a 'Properties' tab...

The fields the OP is asking about are shown in the properties dialog, invoked from the command button on the tasks tab. I think you need BOINC v7 to see it, but I don't know exactly where in the development cycle it appeared.

OK, yeah right the Properties "button". [Duh]

On this " Specifically, if I am in one of my micromanaging moods, is the virtual memory size the amount of RAM held if I were to suspend a task to run another and thus unavailable to BOINC or the system as a whole?"

Depends on if "Leave application in memory, when suspended" [LAIM] option is on, and if the task is still to reach first checkpoint save or is past it. If LAIM is on, a suspended task will always stay in memory, but eventually the OS will move whole or part to the VM if memory is needed for something else. If LAIM is off, a suspended task will be unloaded, freeing up RAM. Not a good idea, as then if checkpoints are far apart, the unloading looses all the progress at resume back top the last good checkpoint, plus chances are, the task has to be fetched from disk again, which can be slow on projects such as Clean Energy. At any rate, always got LAIM on, except during Beta testing to find out if tasks adhere the the interval write setting and if stop/resume does not cause a task to fail.

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Coelum Non Animum Mutant, Qui Trans Mare Currunt