My host is Mac OS X 10.6, and on my VWware Fusion, I have Windows 7 and Windows XP as my guest. I can drag and drop files between my guest and my host, but not between my guests (cannto drag and drop files between Windows 7 and Windows XP). Is it possible?
No you cannot as of, and up to VMWare 4 drag and drop files between VMware guests directly. VMware's tools are only noted to support drag and drop between the guest and the Host Operating system (a.k.a. the Mac in this Case), there is no mention of guest to guest support for drag and drop as noted in the VMware fusion documentation.
That quoted above is likely why drag and drop is not working between your Windows 7 and Windows XP guest virtual machines and that is because it is simply not supported.
A quick fix is to drag the files to the Mac host first, then drag to the other VM. Otherwise setting up File Sharing between the VMs may be the best way to transfer files directly between VMs without having to go though the host first.
Are you using Fast User Switching on XP? If so, you need to turn it off.
Are you using the current version of Fusion? If not, then upgrade.
Do you have VMware Tools installed in both VMs? If not, then install them.