Based on one person's blog, it definitely appears possible (and legal? ) with SBS 2K3 Premium --> http://msmvps.com/cgross/archive/2004/08/06/11375.aspx
Also from a sqljunkies blog (it's an old on though, I think it' kent Tegels http://sqljunkies.com/WebLog/ktegels/articles/852.aspx) -->
Q: When I have Small Business Server 2003, which version of reporting service I can use?
A: I believe SBS Enhanced includes SQL Server 2000 Standard version, in which case you would use the Standard version of Reporting Services.
Maybe talk to yuor local MS partner?
HTH,