If you take down an old computer, you could use the small hard drive as a multiboot toolbox for rescue, etc. Instead of using it for other stuffs (https://www.youtube.com/watch?v=jEzXjJN1RH0
If you wanna do a multiboot toolbox rescue (that is very usefull), here's a quick guide.
I'm gonna use Easy2Boot, I found the online documentation quite confusing.
1 – Format your hardrive to NTFS.
2- Go to the following link http://www.easy2boot.com/download/
3- Download : E2B+DPMS (You could also take the drivers DPMS of Windows XP)
4- Extract the archive into a new folder.
5- Launch in admin mode the script : MAKE_E2B_USB_DRIVE.CMD
6- Choose your options
7- Then you just have to add new ISO in the corresponding folder of your new hard drive.
8 - Everytime you want to add new ISO, you should make them "Contiguous", or they have a high probability to not be launched. If you want to do so, you have to launch the script MAKE_THIS_DRIVE_CONTIGUOUS.cmd
If you want to install Windows ISO on UEFI, you would have to convert the ISO (Check the Easy2Boot website).
You can also create a folder for personnal storage and copy every things you want inside without breaking the previous configuration.