XP Won't cache web sites

Microsoft Windows

Can anyone tell me why XP will sometimes save a Web-site
in the cache file so I can view it offline and sometimes
no matter how many times I visit that site it will not
show up when I'm offline. I need to have a large number
of sites available offline to demo a program I'm selling.
I have maxed my cache right to the end so that isn't the

You can't cache web sites that have dynamic content such as .asp, .aspx