Crystal is incredibly powerful for web based reporting. You have 2 options that I can think of off the top of my head:

1) Configure your web server with Crystal to allow opening a report based on web address (e.g. http://yoursite/somereport.rpt link will allow user to view report using small activeX component, or in java, or in javascript, or in html frames or no-frames). I use this for one particular report and it is great. Uses NTFS security for restricting access.

2) Create ASP pages that utilize the Crystal web engine to interact with a report. This works similar to the option above, however it allows more customizations and interactions with the report. You can even create reports dynamically using this method.

If you really want to use Crystal you are going to be well-off to order their developer's manual. I had to stumble through everything blind searching out on the web and I wish I had the manual instead. Cheers.