AnandTech has a comparison of the new Intel quad-core "Harpertown" Xeon vs. the AMD quad-core "Barcelona" Opteron. The Harpertown CPUs are a 45nm part, and they have a 1600MHz FSB and 12MB of L2 cache. For the several different benchmarks featured in the comparision, the Harpertown has a pretty big advantage over both the older Intel quad-core Clovertown and the AMD Barcelona.
"Intel announced that in its largest configuration, Nehalem (2H 2008, 45nm) will feature 8 cores on a single die, each core supporting 2 threads per core (welcome back Hyper Threading) for a total of 16 threads per physical chip"
DailyTech has more details about Intel’s upcoming architecture here. This is all pretty exciting for SQL Server 2005 and SQL Server 2008, with Microsoft’s policy of licensing by CPU socket rather than by core. You could see a 2 socket server with up to 32 processor cores by late 2008.