Upgrading iMac G3 memory
Do not worry about getting one that is specifically "for iMacs." Any 168-pin PC 100/133 chip should fit just fine.

I have been working with several iMacs over the last few weeks. From my experience with them, a slot-loader seems to max out at around 1GB (two 512mb chips.)

If your RAM is not working, you likely got a bad chip. See if you can exchange it for another one.