Yup. I use Vista x64 and it's been running fine. The only problem I ran into is that for some reason it won't let me open the Users/MyUser/Documents directory when I go to browse for folders, so I couldn't create a campaign there, for example. I think it has to do with the fact that DM Genie won't let you see system folders.
I managed to work around it by sharing my Documents folder, mapping it to a network drive, then using the network drive to hold my campaign data. An easier workaround would just be to use a directory outside of Documents (like C:\DMGenieCampaigns).