PC Internet telephone Echo problems

[IR]

I’m testing PC-Telephone to make PC to PC calls over the Internet. My problem is echo. My reception is good however the person that I’m calling is getting an echo. Any suggestions would be appreciated.
My computer is a Compaq EN series, onboard audio, ESS AudioDrive 1 350 MHz, 64K Ram, Windows 98, AOpen 56K speakerphone PCI modem, using a headphone with speaker attached. The computer getting the echo is a Dell 650 MHz on Rogers High-speed cable.

Thanks in advance