you can install 7.0 from HDA to HDB without any problems.
download the iso inside it there are scripts in the install/vinstall dir that will facilitate this.
I read the readme in the dir with that script and followed the instructions, didnt work.
Unless i totally misread the whole thing, the vinstall script was trying to use gzip to decompress the initrd.lz instead of lz compression. So i tinkered a bit, after i got decompression working it was looking for an ext2 file system and not finding it. Maybe someone should take a look at those scripts before release.
All together i spent about 4 hours futzing around to avoid a 15 minute walk to the drug store for blank cd's. I had to go out today anyway to go to work and got some and installed 7.0 and all i have to say is WOW!