Works for me. My Win 7 box has a 192.168.2.3 IP and shows XP Mode IP as 192.168.56.1 while XP Mode window shows it as 192.168.2.4. I can ping either 192.168.56.1 or 192.168.2.4 successfully.
ipconfig /all from XP Mode window:
Windows IP Configuration
Host Name . . . . . . . . . . . . : VirtualXP-26583
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Mixed
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : router
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : router
Description . . . . . . . . . . . : Intel 21140-Based PCI Fast Ethernet Adapter (Generic)
Physical Address. . . . . . . . . : 00-03-FF-01-1C-61
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 192.168.2.4
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.2.1
DHCP Server . . . . . . . . . . . : 192.168.2.1
DNS Servers . . . . . . . . . . . : 192.168.2.1
Lease Obtained. . . . . . . . . . : Thursday, August 26, 2010 9:47:07 PM
Lease Expires . . . . . . . . . . : Friday, August 27, 2010 9:47:07 PM
ipconfig /all from Win 7:
Windows IP Configuration
Host Name . . . . . . . . . . . . : Dell-P370
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : router
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : router
Description . . . . . . . . . . . : Broadcom NetXtreme 57xx Gigabit Controller
Physical Address. . . . . . . . . : 00-11-11-E1-1F-77
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.2.3(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : Fri Aug 27 2010 4:14:35 PM
Lease Expires . . . . . . . . . . : Sat Aug 28 2010 4:14:35 PM
Default Gateway . . . . . . . . . : 192.168.2.1
DHCP Server . . . . . . . . . . . : 192.168.2.1
DNS Servers . . . . . . . . . . . : 192.168.2.1
NetBIOS over Tcpip. . . . . . . . : Enabled
Ethernet adapter VirtualBox Host-Only Network:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : VirtualBox Host-Only Ethernet Adapter
Physical Address. . . . . . . . . : 08-00-27-00-24-ED
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::f0a0:2cd:bc9:c2de%16(Preferred)
IPv4 Address. . . . . . . . . . . : 192.168.56.1(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . :
DHCPv6 IAID . . . . . . . . . . . : 369623079
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-12-B4-CC-2B-00-11-11-E1-1F-77
DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1
fec0:0:0:ffff::2%1
fec0:0:0:ffff::3%1
NetBIOS over Tcpip. . . . . . . . : Enabled
See this article for info on getting Networking to work in XP Mode so you can access other computers on your local network:
Networking and Using Windows XP Mode - Windows Virtual PC - Site Home - TechNet Blogs
I just did this last night (see the thread here):
Win 7 XP Mode No Home Network Access