4
How about exploring XOOPS to learn how and where it fetches things?
Now take a look:
As you can see the login is a block!
Its look is rendered from a block_login.html
Since the login(block) is part of the system .........
Rings a bell?
modules/system/templates/blocks
Here you'll find its htmlfile, which you can redesign.
Offcourse you can do this also from xoops/admin itself by cloning the templates.
Grtz., Shine