You don't have any access to the iPad's file system. Apple lock down their idevices pretty tightly. However, that does not mean you can't view your own HTML files using an alternative method.
Have you tried Dropbox? Free cloud storage. You can put anything you like on there and the free app can be used to browse any HTML files you put on there with ease.
Goodreader is also an excellent "swiss army knife" file viewing tool, which can integrate with any number of storage services, or sync content on via iTunes. Again, this would be a fairly simple way of doing what you want.
If you want to actually save pages you visit from Safari to read later offline, then that feature will be baked right into the Safari app when IOS6 is released, estimated to be around September time. You will them be able to add pages to your "reading list" and save them for offline viewing later. At the moment, the features in IOS5 only allows on-line reading later.
If you really want full access to the iPad's file system, your only option is to jailbreak. Head on over to our hacking section if you want to find out more about that.
Hope that helps.