Depends on what timings are set in the SPD. The PC133 might have CL2 at 100MHz, and two modules mean interleaving is possible (if the chipset can do that).

i440BX can only run its RAM synchronously, so FSB=RAM. With a P3-450 you're running RAM at 100MHz in any event.

Now, the ratings at a given speed (PC133 CL3 etc) are less interesting than the actual ratings of the chips. Look for the last character on the chip code, it will be something like -75 (7.5ns, normal for PC133 CL3).

Now:
100MHz CL3 requires 10ns
100MHz CL2 requires 8ns
133MHz CL3 requires 7.5ns
133MHz CL2 requres 7ns (or 6.5ns according to some sources)

As you can see, 133MHz CL3 requires shorter timings than 100MHz CL2, so any DIMM that can do 133MHz CL3 can also do 100MHz CL2.

Ignore whatever the SPD tells you (SPDs in the early SDRAM period were notoriously inaccurate and sometimes entirely missing), just set that 133MHz CL2 RAM to run at 2-2-2 timings and you'll be fine.