Remote Capture in Windows XP

Here's a setup that I use, which you might try (Instructions are based on Windows XP Professional SP3 using Wireshark 1.4.2, and WinPcap 4.1.2):

On the machine running the remote packet capture daemon:

1. Create a local user account for remote capture authentication: Start -> Control Panel -> User Accounts -> Create a new account -> Advanced -> Advanced -> Users (right-click) -> New User -> [Fill in details] -> Create.
2. Configure rpacpd as a service: Start -> Administrator Tools -> Services -> Remote Packet Capture Protocol v.0 (experimental) (right-click) -> Properties -> Log On -> This account -> [Fill in the account details from step 1] -> OK.
3. Start rpcapd as a service: Start -> Administrator Tools -> Services -> Remote Packet Capture Protocol v.0 (experimental) (right-click) -> Start.

On the machine running Wireshark:

1. Configure the capture options: Capture -> Options -> Interface -> Remote -> [Fill in details]* -> OK.
2. Choose the remote interface: On the capture options window, the remote interfaces are in the drop-down list in the upper right corner. Pick the one you need.
3. Choose the remainder of your capture options, including remote settings, as needed, then choose Start.

*NOTES:

• The Host is filled in as the remote IP address only, with no rpacp:// prefix or anything else.
• It is not necessary to fill out the port unless you have changed it on the remote machine from the default of 2002.
• Choose Password Authentication, then fill in the remote username and password credentials.

For more information on WinPcap remote packet capturing, try here.

Did you try this:
rpcap://IPADDRESS/\Device\NPF_{INTERFACE INFORMATION}

BTW
I'm running Wireshark version 1.5.0 and WinPcap version 4.1.2.

...the error "Can't get the list of interfaces: Logon failure - unknown username/pwd (I'm using the domain admin pwd and not local admin- hope this will work).

Sound like a clue, doesn't it?