You need the disc(s) that were original to the system. Since, you didn't create the "restore discs", then you're left wanting or whatever. If this is an OEM type system, then ask the makers for the restore discs for some small cost. Provided they still have them, it's worth asking. Otherwise, you then need the retail version of Vista or generic DIY type OEM version. There is no other way around this that's legal and/or proper. You can eBay or google for so-called restore for your OEM model PC if popular they maybe available.
can windows 7 be uninstalled ad my vista ultimate reinstalled from backed up files or a download. i do not have the disk it was installed with. it came already installed.