"an ibm aptiva e3n w/ amd-k6-2, win 98, has problem with the hard drive. looking at replacing with a western digital 40gb model wd400bbrtl. All we want for the machine is simple web surfing and word processing. will this work?"

I'll write yes. If the IBM doesn't like the over 32 gigabyte drive, use the LIMIT SIZE (it's name varies) jumper to get 8.4 GigaBytes(GB) and it should work fine and still be larger than what the machine came with.