More than likely you motherboard only supports 2 single sided dimm's or 1 dual sided dimm, not both. It should probably work with 2 - 1GB single sided dimms. You can check Crucial's memory configuration tool on their website to see what is actually compatible with your mobo.
I just looked at reviews of this on NEWEGG and another buyer has the same issue. He says exactly what you said.
The machine will only take 2 of each respective side.
I wish Kingston or e machines would have explained this.
Thank you, everyone.
"I already had 1GB of PC2-4200 memory in the machine. The machine will see either stick individually, but if both are installed, it will only see the Kingston RAM.
The Kinston memory is single sided. The one in the machine is dual sided (chips on both sides).
Neither NewEgg nor Kingston or a couple other sites I looked at say anything about x8 or x16 or single or dual-sided or dual channel"