[CentOS] centos4 install freezing on Compaq Workstation ap250

Hello,
    I'm trying to install Centos4 on a Compaq Professional Workstation 
AP250. I'm doing this via serial terminal as this box does not have a 
monitor and install is getting to the running of /sbin/loader then it 
freezes. I've tried
linux text console=ttyS0
and added combinations of:
nousb
noathlon
apm=off
acpi=off
nothing is working. Some urgency! Any help appreciated.
Thanks.
Dave.