Question : xp sp2 clients wont log or ping server 2003

We have just made some config changes to a Small Business Server 2003. it had 1 NIC and we have noe set it up using 2 NICs.
We have also setup the oruter so that it connects via 1 NIC and the internal PCs connect through the 2nd NIC. All standard practice and I have done this all before.

The 2 NICs are installed and working, and the server can access the internet!

The problem now is that none of the desktop PCs can access the server.
They cant ping ip or name.local, they wont log on, but they get a IP address which is correct and is registered in DHCP and DNS.

Any suggestions would be appreciated.
thanks!

Answer : xp sp2 clients wont log or ping server 2003

we ended up rebuilding - there was no AV on this server and it was in a bit of a mess... now its ok