3
You don't need to use tables. The only essential part of the theme is the content, not how it is presented... presentation is entirely up to the designer.
The content that you have to work with is:
Main page content:
<{$block.content}>
'Blocks' of content:
<{$xoops_lblocks}>
<{$xoops_rblocks}>
<{$xoops_clblocks}>
<{$xoops_ccblocks}>
<{$xoops_crblocks}>
Traditionally, because of the name and user expectation I guess, those blocks of content have been positioned in left, right, center left, center center and center right positions. But there is no reason why you can't put that content wherever you want, put all of them in one area if you like, in whatever format... i.e., tables are not necessary.
Look at existing theme.html files to see how to get access to the content in the blocks and main page.
Good luck
Rowd