you can normally install a 64 bit VM on a 32 Bit Host -- I had W7 X-64 up and running on an XP Host.
What you MUST have to run a 64 bit GUEST VM is that the CPU must support the Intel VT technology and it must be ENABLED in the BIOS. (Equivalent for AMD although I'm not sure of what they call it).
Note also that since the HOST is a 32 bit system it's max RAM is 4GB so your 64 BIT GUEST won't be able to have more than (4GB - HOST RAM) amount of RAM allocated to it -- shouldn't matter too much -- in my XP testing days I ran W7 x-64 VM's with 1 GB RAM on a 4GB XP Host.
For vmware have a read of this
How to Install 64 Bit Guest OS on 32 Bit VMware Workstation
VBOX has similar constarints.
However IF your BIOS is OK and most modern Bioses are -- you shouldn't have any problems running X-64 VM's on 32 bit hosts.