Help needed: Why does my web page hang?

I am a php newbie developing a shopping cart for a web site. If I start at http://www.arylis.com/test/page1.htm and click a few buttons, the response is prompt at first, but eventually the web page seems to just hang, and takes half a minute or so to respond. Sometimes I get a timeout error message. The computer is still useable for other tasks. Just the web page hangs. This happens on my Win ME localhost (my own computer), and also on my ISP's remote Windows server. Is this a streaming or buffering issue? Is it a php bug? Any ideas how to fix this? I hate to keep customers waiting! Thanks Paul in Canada