So partitioning through Win 7 would not wipe the Vista files?
Ummm, I did not say that. The hope when using any one of those utilities is that no files will be damaged or lost, but there is no guarantee of that. Any time you mess with the partitions, there is a risk all the data will become corrupt. These programs try to minimize that possibility but stuff happens. The hard drive could hiccup or a drunk hits a power pole and takes out your power, or the layer of heat trapping dust over the CPU heatsink finally causes the CPU to overheat and shut down (with a crash). Who knows? Murphy's Law
Anyway, I think you are focusing on something not important. This is now a Windows 7 machine. There is no need to worry about Vista files. The only concern would be data files (personal pictures, songs, word documents, etc.) and programs that your friend downloaded (or bought on disk) then installed on the Vista machine. You said you already backed up the data files. For the programs, he can just download and install them again - though this time using Windows 7 so the Windows 7 Registry is properly configured. With that Vista disk serving now as a secondary drive
for additional storage, assuming resizing the partitions leaves all files in tact, the Vista files will remain on that disk in tact too - should your friend decide to return that drive to the old Vista machine. Though in my opinion, those old Vista files are just hogging up disk space.
He would just like to have the option to mess with Vista in the future
That's fine but not on this new computer. As noted before, it most likely is an OEM license for Vista, therefore it can only legally be run (booted to) on the old Vista machine. The Vista files just sitting there on this new secondary drive are not bootable (because the drive is not a boot drive). Therefore, no license violation issues. That said, should he return that Vista drive back to the Vista machine (or buy a new hard disk for the old Vista machine) he can just reinstall Vista on the old Vista machine using his Vista install disk and license.
There is nothing in Vista that is better than Windows 7. Window 7 is what Vista should have been (Vista 2.0, if you will).
He should give up on Vista and if the old machine someday gets up and running there would always be Linux or a newer OS from Microsoft!
Or put that drive back in the old machine and just run it as a Vista machine (perhaps as a backup machine), or as you noted, experiment with Linux, always a good learning experience. As for a future OS from Microsoft, probably not a good option. Part of XP's bad rap came from Microsoft's desire to please customers who wanted XP to support their legacy (old) hardware and software. Sounds good, but old stuff (especially pre-XP stuff) is typically less secure. So while Microsoft was successful in making XP support legacy stuff, that left XP less secure for which Microsoft was bashed relentlessly for the next 10+ years (even though it was bad guys who created the security mess, not MS).
So MS, tired of being bashed for something not their fault, has vowed to put security first and not legacy support and I applaud them for that. Windows 7 was designed to support current and future hardware and software and not old hardware and software. Windows 8 and future offerings will do the same, so it is likely that old Vista hardware will not be supported by future MS operating systems - that is, the makers of that old (obsolete and no longer in production) hardware may not create drivers (expend resources with zero returns) for future operating systems. They would rather you buy their new hardware that comes with new drivers.
And I am okay with that because, being a hardware guy knowing and appreciating that advances in hardware technologies continue to advance the state-of-the-art, I will want an OS that can take advantage of those latest hardware technologies - even it means retiring some older, but perfectly functioning hardware.