Question : Cannot ping from exchange 2003 server to domain controller (request timed out)

I have a strange situation.
I can ping any computer on my LAN, except the domain controller (I'll call DC) from my Exchange server (I'll call MAILSERVER), but (the strange part) my server, DC, can ping MAILSERVER. But I can connect to DC's shares from MAILSERVER and all other computer on the LAN can ping DC. Windows firewall is not setup on either box, nor is IP filtering, they are connected to a Netgear GS724T Gigabit switch. Doing an nslookup from MAILSERVER, I get the IP of my DC server. Also, my Outlook clients are getting popup windows saying "trying to connect to exchange server". Below is ipconfig, nslookup, and ping results. Any help would be greatly appreciated.

Windows IP Configuration

   Host Name . . . . . . . . . . . . : mailserver
   Primary Dns Suffix  . . . . . . . : mydomain.com
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : mydomain.com

Ethernet adapter Local Area Connection:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Intel(R) PRO/1000 MT Network Connection
   Physical Address. . . . . . . . . : 00-13-72-F7-9F-06
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 10.10.10.4
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 10.10.10.1
   DNS Servers . . . . . . . . . . . : 10.10.10.2
                                       10.10.10.14
   Primary WINS Server . . . . . . . : 10.10.10.2
   Secondary WINS Server . . . . . . : 10.10.10.14

C:\>nslookup dc
Server:  dc.mydomain.com
Address:  10.10.10.2

Name:    dc.mydomain.com
Address:  10.10.10.2

PING From MAILSERVER to my domain controller (DC):
C:\>ping dc

Pinging dc.mydomain.com [10.10.10.2] with 32 bytes of data:

Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 10.10.10.2:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)

Answer : Cannot ping from exchange 2003 server to domain controller (request timed out)

Interesting item is IP Routing Enabled on your dc.  Are you using Routing and Remote Access on this machine.  Is the firewall associated with that on?