MCP is NVIDIA's acronym for Media and Communications Processor. The "T" version simply means "Turbo," which in this case does not translate to higher speeds, but to a more extensive range of functions.

Southbridge	Media and Communications Processor	Media and Communications Processor Turbo
Alias	MCP	MCP-T
Image
Hard Disk Controller	UltraATA/133	UltraATA/133
USB Controller	6 Ports USB 2.0/1.1	6 Ports USB 2.0/1.1
FireWire Controller	-	Conforms to IEEE 1394a
Network Controller	Single: NVIDIA Media Access Controller (MAC)	Double: NVIDIA DualNet : NVIDIA & 3COM Media Access Controller (MAC)
StreamThru	Yes	Yes
Sound Controller	AC97 2.1 2, 4 or 6-channel 20-Bit Out, 16-Bit In ANR & CNR Support SPDIF-out	AC97 2.1 & NVIDIA APU (Audio Processing Unit ) Hardware DirectX8 Processor Dolby Digital 5.1 Encoder 256 voices 64 3D voices 32 Bit Mixer 2, 4 or 6-channel 20-Bit Out, 16-Bit In ANR & CNR support SPDIF-Out

Basically, the new MCP-T differs from the MCP in three aspects: the MCP-T offers an integrated FireWire controller and a second network controller, as well as NVIDIA's Audio Processing Unit (APU). And be careful to note that MCP has different meanings with the nForce and the nForce2. With the first nForce, the APU was included in the simple MCP, whereas with the nForce2, the MCP-T is required.