You can't add SSE2 to a processor that does not have it, because it requires hardware support. Intel added SSE2 to Pentium 4 Williamette back in 2000, but AMD did not until Athlon64 in 2003. No socket A (socket 462) AMD chip has it.
Without SSE2 you cannot run the later versions of Firefox, Chrome, Flash, or Office 2013 because those developers decided to reduce the size of their programs by eliminating the backup non-SSE2 codepath. Either you can fork those from the last version that did not require SSE2, or you can create an emulation layer that translates calls to SSE2 to something using SSE, MMX or x87 FPU, which would be much slower.