pingable means from outside, right. So are there any firewalls between outside and xen?
have you tested any other service, like http? try that.
does your xen box get/answer the ping? tcpdump -i eth0 icmp. Do you see any echo/echo-replys generated from your box?
According to your first mail, eth1 is the if with the public interface! Why are the addresses configured on eth0?
Another thing is that your gateway/Dom0 ip is looking exactly like a transfer network,
75.126.153.176/29 for routing purpose. You should get some information from your provider how exactly the routing setup is.
I dont believe it is xen, i have a similar setup.