That depends on several things.
Since Pentium 2 and Pentium 3 Katmai both use the same interface type (SECC/Slot1) you can physically insert it. Most Pentium 3 motherboards support Pentium 2 also.That depends on several things.
Since Pentium 2 and Pentium 3 Katmai both use the same interface type (SECC/Slot1) you can physically insert it. Pentium 3 also comes in Socket 370, which is in no way compatible with Pentium 2 due to a faster front side bus (100MHz). Most Pentium 3 motherboards also support Pentium 2, and a very small selection of later model Pentium 2 motherboards can be made to support Pentium 3.
However, if I were you I’d just lie to him and tell him to get new equipment that actually has practical use