XP strange networking problem

I have a HP Pavillion desktop with XP home edition. The rest of the
office desktops are running XP professional and joined a domain
controller. This XP home is configured before I came to office. I have
no idea how it set up but it works. One day I decide to add more
memory since it only has 512M. After I took out one 256M piece and
installed a 1G stick the network stopped working after reboot. When I
look at the network connections there are 4 listed, local area
connection, 1394 net bridge, Nvidia Nforce (mcp) bridge, and Mac
Bridge Miniport. When I use ipconfig I don't see any valid ip address.
So I go to local area connection property page and set a static ip
address. However I still can't ping the router. After some trying I
disabled, then enabled Mac Bridge Miniport the internet starts
working. I get a valid ip address on this miniport bridge from dhcp
server. Then I try to figure out why internet wont' work after reboot.
It appears that the MCP service wont' start automatically even the
start option is automatic. I try to start the service from the service
control panel. The service can start but the internet still won't
work. The only way I can make internet working is to disable Mac
Bridge Miniport, then enable it. I am totally lost with this strange
configuration. Anyone has idea what I am dealing with and how I can
fix it? Thanks.