If I remember correctly, run the install, but have a floppy ready. I believe that it wil ask you what drive you want to use for the install. Select your floppy (obviously) and it will install it. From there, you simply insert the disk while the PC is shut off, or while you are in your BIOS screen and boot. It will load memtest and immediately begin to test. There are some test selection options, if you choose, otherwise it will test in loops. The link below is to a very good discussion on using Memtest.
http://www.bleedinedge.com/forum/showthread.php?t=442