Likely your graphic is wrapping to the next line since it isn't small enough to fit on the same screen with the table. You can test this by making the graphic really, really small (or the table skinnier) and seeing what happens -- does stay on the same line now?

The easiest way to position graphics on a page with tables (IMO) is to create cells for the graphics, then insert the graphics inside. The cells won't wrap, they'll just extend to the right off the screen, and you can merge cells together to get the right mishmash of grid shapes. (Like 4 cells on one side and 2 on the other.)

Working with tables in raw HTML stinks -- this is one area where having a program like Frontpage or HomeSite can really speed up your work.