It has been such a long time that I don't exactly remember. But if LLevram has archives going back to the beginning of Wiz 8 (the last days of Wiz 7), then you will find explanations by me and others.As I dimly recall ...
1) find a Wiz 7 folder full of .BMP portraits
2) make a copy of this folder in case you screw up
3) find out the EXACT size of the bitmaps - 100x120 in one folder, and one other size in the other folder.
4) in a WORKING directory BUT NOT in the WIZ 7 directory take the .JPG or .GIF you want to import, trim to proper size, save as a 256 color .BMP
5) OMG WHAT HAPPENED TO THE COLORS !!! Your ex-jpg's 16,000,000 colors was reduced to a palette of 256 colors. Use your favorite photo-editing software to adjust the .JPG's colors, or use MS Paint to fix the .BMP pixels one by one.
5) NOW go to the Wiz 7 bitmap folder and open an existing portrait with Microsoft Paint. I suggest an ugly one.
6) click on Edit/Paste From... then select the new portrait from the WORKING directory. Be sure the sizes match.
7) OMG WHAT HAPPENED TO THE COLORS !!! Wiz 7 has a separate palette of 256 colors that will not match your new bitmaps set of 256 colors.
8) if it looks OK, save. If not, return to step 4).
9) consider starting with a new picture if your first one Just Won't Convert Right.
10) One of the colors is "transparent" to allow the background to show through. Eliminate that from your .BMP wherever necessary. Keep it around the outside if you wish.