Do you know if your disk uses the gpt-table, or ms-dos? From what you are writing I assume that you have other working distros running on the same disk/pc? Is that correct? Like Crunchbang or some other distro with GParted? I seem to remember you from the #!-forum, so I assume that you have a working #!-install on this pc. If you do, then launch Crunchbang....
Then launch GParted. Select the disk in question(if you got more than one disk). Then look at the menu on the top. Click "View", and then mark "Device Information". Now you should get the Device Information in the left pane of your GParted-window... Look at "Partition Table". If it says "gpt", then you are probably out of luck, because the current installer doesn`t support gpt. If it says "ms-dos", then you should be able to install VSIDO...
If it says "gpt", you would need to delete all partitions and create a ms-dos table... You would loose all your other installs, and have to start from scratch, but it would work for all the distros.... So whether to do it or not, depends on whether you want to start from scratch with all your distros, or if you find it better to wait until the VSIDO-installer supports gpt. If Vastone gets the Debian-installer to work with VSIDO, then you will be able to install VSIDO without touching your other partitions or distros... It`s up to you:)