Many sites place the menu in a frame at the left of the page. Since many of us will be making pages for our students to access and many of these students may be accessing them from home or dorm through a modem, size is something that must be taken into consideration. This is a very rough estimate. Using this formula, a 30K graphic would take 32 seconds to download. A typical 30-35K graphic may download in less than a second on a 56K or T1 line but it would take over a minute to download using a typical 14.4 kbps modem.
Larger graphics take much longer.
I try to keep the maximum size of my graphics to under 30K. After you have put your pages together, add together the size of your text and graphics. Try to keep the total size down. The most important part of your page is the top 300 pixels. This is the part that people see first so this must be the part of the page that will grab and hold their attention. The human eye only can distinguish about 32,000 colors.