VMWare virtual machine (XP) size growing... why?

I have just installed Windows XP with VMWare Fusion (2.0.6) and every time I shut down VMWare and check the size of the virtual machine back in Finder in OS X (Snow Leopard) it has grown by 2GB or so. Why is it doing this and how can I stop it? (It's now 8GB+ even though there is no software installed on the Windows side).

I am running these on a late 2007 iMac.

Thanks!

No, none- that's why I don't understand the rapid growth- tripling in size since installation...