I suspect that part of the problem is the large number of nested tables in the layout. IE will not display a table until it downloads all the content for it and finalizes its calculations for that table's dimensions. When you have tables within tables within tables, it therefore does not display anything in the outermost table until all of its contents and all the contents of all the inner tables have been downloaded and run through its rendering algorithms.
While using the tips from my previous link to decrease the total page size will help, redesigning the page structure to limit the amount of tables and especially table nesting will help IE to start rendering things as they are downloaded, rather than being blank until all the data arrives. (In other words, it's time to learn how to lay out pages with CSS and semantic HTML markup instead of nested tables -- which by the way will probably improve your search rankings.)