Xbox 360 Announcement
A quick bite of the specs:
Custom IBM PowerPC-based CPU
Three symmetrical cores running at 3.2 GHz each
Two hardware threads per core; six hardware threads total
VMX-128 vector unit per core; three total
128 VMX-128 registers per hardware thread
1 MB L2 cache
Custom ATI Graphics Processor
500MHz processor
10 MB of embedded DRAM
48-way parallel floating-point dynamically scheduled shader pipelines
Unified shader architecture
There's an official website
here