Not the same serial (=impossible), but you need one with the same stepping all right. Win2K or NT will tell you the stepping: system properties / advanced / environment variables / scroll down in system variables.
---- Owner of the only Dell computer with a AMD chip
And then download the "Pentium III Processor Specification Update"
"This was no boating accident"
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Have a look under (W2K) administrative tools/computer management/system summary: It should read something like this:
Processor x86 Family 6 Model 8 Stepping 3 GenuineIntel ~733 Mhz
except yours will say 800Mhz. Here you find the "Stepping" information. Just make sure its the same stepping number. Then plug in into the second cpu socket. Load w2k and once your loaded hit ctrl-alt-del and bring up task manager. Go to the peformance tab and make sure both cpu's have registered. Occasionally w2k will fail to recognise the second cpu, if so just format and reload, you should be fine. Good Luck.