Cannot use Mcaffee Virus Scan on Acer no

Hi,
Some of my Acer Travel Mate notebooks were installed with PC CILIN Antivirus s/w when I purchased them. I wanted to install McAfee Total Virus Defence (latest version) into them as per corporate requirement. The O/S is Win 98 SE. The system boots and gets into Windows. But at the last stage of the booting (when the Start Icon appears)the system hangs indefinitely.
I tried:
1. uninstalling the previous s/w.
2. Formating the disc and installing McAffee alone.
It simply did not work.
COntacted Microsoft, Acer and Mcafee also. No proper reply from any of them. Can anyone help me?