Windows – Browsing \\computer\share fails, but net use \\computer\share works

I've had mixed results with using Windows Explorer to browse remote file shares.

The setup:

• I'm at work on Windows XP SP3
• Files are at home on Windows XP SP3
• Two separate VPNs are available to access my PC at home
• corporate OpenVPN (10.1.2.3)
• a Hamachi/LogMeIn connection (5.1.2.3)

With respect to my problem, it doesn't matter which IP I use. They both perform exactly the same way:

I expect that if I open Windows Explorer and type in \\10.1.2.3\Shared I should be interrupted with a challenge for credentials, and then be able to interact with the files in the share. However, I just get that annoying dialog, "Windows cannot find '\10.1.2.3\Shared' Check the spelling and try again, or try searching for the item …"

However, I can take that exact same computername/sharename and with net use I can:

net use * \\10.1.2.3\Shared * /user:homecomputername\username

with this result:

Type the password for \\10.1.2.3\Shared:
Drive Z: is now connected to \\10.1.2.3\Shared.

The command completed successfully.

I can then access the files in Z: in Windows Explorer which was my original intent.

Even after Z: is already mapped and the credentials are cached I still cannot bring up \\10.1.2.3\Shared in Windows Explorer.

Why does the latter work, but not the former?

Edit: Other services work fine, such as RDP. (I have a problem in which I can't SSH home, but I'll consider that separately.)