See a review of web deployment options for Crystal Reports at:
The Crystal Reports® Underground
If your company has a Citrix or Terminal Services server, you could deploy a simple viewer.
Finally, you may want to rethink your assumptions about what your users actually need (e.g. ad-hoc parameter entry). Many users actually prefer a solution that pushes Crystal Reports content to them on a periodic/exception basis, or provides auto-refreshing web dashboards. This can be achieved with simple and inexpensive technology.