Why does MySQL chew so much virtual memory on Windows?

Hi All,

Have a fairly busy MySQL server using MyISAM and InnoDB tables on Win 2003 with plenty of available RAM (total 4GB, with about 1.5GB unused) which is using a massive amount of virtual memory despite having tweaked MySQL to use as much memory as it needs. RAM usage never gets much above 400MB, however Windows is reporting that MySQL is using a massive 1.5GB of virtual memory.

Most other processes use a similar amount of RAM and virtual memory, so why would MySQL be using 4~5 times more virtual memory than physical memory? Especially when there is so much free physical memory?