Hi Mihkel,
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr syscall mmxext 3dnowext 3dnow up
Your processor does not have SSE, but it does have 3DNow! extensions. Later Athlons have both, so I guess it's not a case of needing one or the other for these optimisations to work.
Cheers! Daniel