Windows can't ping Unix

we need more info. what is the exact error message? anything in event log on xp or 2k boxes?
any firewall?
here is some interesting reading about using ping:
mskb article 314067 How to troubleshoot TCP/IP connectivity with Windows XP available at support.microsoft.com

Knowing the flavor of unix usually helps pointing you in the right direction. However, they are very uniform when it comes to networking. Try these steps:
1) Edit /etc/hosts and add entries for your windows PCs
2) Edit /etc/resolv.conf and make sure to include entries for your primary and secondary DNS servers
3) Make sure you share a common gateway between your PCs and your UNIX box. You might need to add a route ('man route' to learn more).

This appears to be a tipical non-trusted server issue. If you add entries in /etc/hosts unix box will learn to trust your PCs. To keep delay to a minimun, setting your /etc/resolv.conf and setting up a route/gateway will definately help.

Hope this helps!

Jose Lerebours

Here are the knowns -
1. DNS is working on MS - unless you are using ip addresses.
2. MS can surf the Net.

Possible problem areas -
1. Bad arp cache on the MS servers.
2. Mis config on the routers.
3. Netmask is set up wrong.
4. Some other server interface may have same ip address.
5. Firewall on the XP/2k boxes.

Possible test -
1. Can you telnet/ftp to unix? Ping is different then telnet.

There are some tools that can be used to sniff the traffic as well.

thanks,