the Ultimate Wizardry Archives installs wizardry 1 into this default directory: C:\WIZARD15\assuming the files are still in that directory, open that folder up with Windows Explorer or whatever. what you are looking for are these three files: WIZ1.COM, WIZ1.DSK and SAVE1.DSK.
WIZ1.COM is the actual program that you run, WIZ1.DSK is the scenario disk (for lack of a better term) and SAVE1.DSK contains all the information about your heroes and their struggles.
all you really need to do to back up your characters is make a copy of SAVE1.DSK and rename it to something like BACKUP1.DSK. easy enough!
now for restoring: let's say you go to battle WERDNA and he slaps your party around leaving all of them dead. just go back to the C:\WIZARD15\ directory and delete your current SAVE1.DSK (the one with the dead characters) and make a copy of BACKUP1.DSK (the one with the alive characters) and rename it to SAVE1.DSK. your old characters are restored!
hope this helps, and good luck with your adventuring!
Willow