Get yourself a 6.4GB hard drive
And where would one find such a small drive today? If you have a collection of old computer stuff, maybe there's a drive available. But it's been a very long time since such small drives were sold.
When youre through playing with VectorLinux, disconnect it, then reconnect the Windows hard drive, and the computer will never know you made the switch.
Okay for an initial tryout, maybe, but all that plugging and unplugging is both a pain in the rear and stressful for the connectors and the cable if it's done often. You forgot about opening the case, which to my mind is the worst part of the whole deal. If you leave it off all the time you get too much dust in there and you may disrupt air flow for cooling. Plus things are louder if they're not in a closed case and you may have some interference with other electronics in the house.
Re: size of hard drive for VectorLinux 5.8 Std
You need at least 4.3GB, 5.0GB is better, 6.4GB is ample, 8.4GB is plenty, 10.2GB is more than enough. (3.2GB is bare minimum)
10 gigs is ample for programs but is most certainly not enough if you have a lot of music files, digital photos, and videos. I just replaced a 200-gig drive with a 500-gig drive because things were getting a little tight on the 200-gig drive.