When I load a page that has several item applets on it (along with images of the items), quite often one or more of the applets appears to be invisible. If I hit refresh, it may reappear, but then another applet my disappear. My customers just think that the item is not available, which is not a good thing.
I have tested this using IE 4.0 and Netscape 4.5 and 4.7, running under NT and Win98, and get the same results.
There are various things that could be causing that problem. To determine if it is a server, codebase, or html problem would require taking a look at the site.