"Has anyone used a Dell laptop as a standalone Linux machine?"
I'd guess a few million or so.
You might be able to use the old desktop as it is. Boot to a network. www.netboot.me
is a neat trick.
Live cd/dvd's and usb's could work. In fact a real install to a usb drive may be fine. Flash drives in the 8G range cost almost nothing.
One may find that running a free virtual machine on a newish system would be excellent to try. It is very easy and safe.