Someone really ought to unify the terminologies used in Windows.
In PerfMon, Virtual Bytes is NOT the same as the VM Size in TaskMan. Virtual Bytes is the sum of committed AND reserved virtual space (including shared pages) of a process. In other words, the reserved range of virtual address space by a process. VM Size is actually the private committed virtual space, the equivalent of which in PerfMon is Private Bytes.
I also find that in PerfMon, Page File Bytes seems to mirror Private Bytes exactly. Is this always true as long as virtual memory is enabled?
Also, Mem Usage in TaskMan is the size of the working set (not limit), which is equivalent of the Working Set counter in PerfMon.