Yes S1 for stepping 1 and S2 is also known as Xeon processor.
A processor number is classified in order by
speed, cache, bus, voltage and then the UL identifier which gives you the step.
So 500/512/100/2.0V S1 is clearly recognized.
Xeon or S2 processors are generally more reliable.
Asus P4P800 SE
Intel P4 3.2 Gig 1024 Meg PC3200 cas latency 2.5
RAID 0 2-36.7 Gig SATA WD 10,000 RPM
200 Gig WD ATI ALL-IN-WONDER 9600XT
6500 Kb bandwith Internet Connection