The SO-DIMM that you want to use shouldn't cause any problems, even though it's the faster PC-133 SDRAM. It should downclock to your PowerBook's slower bus speed. Judging by the shadow (or lack thereof) under each memory module in your photos, the upper SO-DIMM is undoubtedly the original Apple-installed 4-chip, 64 MB module. The "Power Ram" appears to be a 16-chip, 128 MB module, while the Nanya is an 8-chip, 256 MB module. What this means is that each of these SO-DIMMs has a chip density that differs from the other two. The Power Ram's chips have the smallest density, the SEC's chips have slightly greater density, and the Nanya's chips have the greatest density. I always felt that optimal performance in those older Macs was achieved by attempting to match chip densities. I would never have used an original (8-chip) 32 MB DIMM with a newer (16-chip) 256 MB DIMM in one of my desktop or mini-tower G3s. While you'll have 64 or 128 MBs less of total memory installed, I'd prefer to use the Nanya SO-DIMM by itself. If you really need additional memory, you could install the original Apple (SEC) module, but I wouldn't.
As to whether a memory fault is causing the startup problem, I would be more inclined to think that the original (if it is) hard drive is becoming unreliable. A 15 year-old laptop drive has undoubtedly had a lot of use and in an enclosure that doesn't dissipate heat the way a fan-cooled desktop or mini-tower is capable of doing. When the PowerBook does manage to complete startup, how much installed memory is indicated when you select "About this Macintosh" from the Apple Menu — 192 MBs? If so, then both modules are detected and passed the Power-On Self-Test. If memory problems are detected during the POST, you should hear a beep or beeps at startup, indicating a problem.
