What does the SSE do in my AMD athlon do and how do i enable it?

Answer 1

SSE=Streaming SIMD Extensions, originally called ISSE, Internet Streaming SIMD Extensions.
SIMD=Single Instruction, Multiple Data
During the Katmai project Intel was looking to distinguish it from their earlier product line, particularly their flagship Pentium II. AMD eventually added support for SSE instructions, starting with its Athlon XP processor.

Answer 2

Yea, what the first answer said!
Here a guy explains how it enabled;
http://myplc.com/sony/sse_enabling_and_wcpuid.htm

IF, you update BIOS make sure it for your specific computer. Go to your computer's support and find the BIOS and learn how in is updated. IF, the BIOS work, do not update! That what they say.