I'm using Windows 7 I think the release edition or what have you, I'm not sure, but it's not branded so I don't know.
Regardless, it works and acts the exact same way as Vista on my computer in terms of what runs on it and such, only major difference that's visual is the theme(Which actually I don't like, but I'll find a way to theme it, somehow, some day).
You can always use a little mini-partition(~20mb) in like /dev/sda1(Whatever windows turns that into) that's like ext3 for grub, but that's inconvenient..
If you can resize the partition, I'd delete the ubuntu partition(s), then resize the Windows partition to fit the whole space, then just upgrade to windows 7, that way you keep your files yet get the 7.
However, I'm sure it's harder than I said it.