Primary difference between the two, and this sometimes means a big difference depending upon what type of performance you need from your server:

SPARC is a 64 bit processor
Intel XEON is a 32 bit processor

Another difference is that SPARC technology only runs with UNIX/Linux products, and is most compatible with Sun's SOLARIS.

The Intel XEON is built for just about anything, intel is famous for making their chips compatible with the latest technology/OS out there, whether it be the new Windows version, or the newest Linux ports.

As for performance, like I said, it all depends on what type of operation this server will be hosting.