Do you run Crystal on your SQL server now?  If so, Reporting Services should not be a problem.  40 people in our class were running RS on their servers w/ SQL and putting RS on another server was not even a topic that was brought up in the class but I have sent Mr. Homnick, http://www.homnick.com, an email expressing your concerns.  Besides, you can import any existing Access or Crystal report into Reporting Services.  The advantage is that you have it all wrapped around Web Services and XML.

As for an additional server, with the price you pay for enterprise licenses of  Crystal, you can buy three servers with SQL and Reporting Services.

Perhaps that since you are already knee deep in Crystal, RS is just not the solution for you.  However, it is very much worth looking into for those that are open to other reporting platforms to work with their existing SQL Server.  It is economical and .NET ready.