Strange Remote Desktop Problem-- won't connect over LAN, will over 'net

[pervnerve]

Hey all.

I've found hundreds of complaints over google and in forums about how people's RD works over LAN but not the internet. I have the opposite problem: I can connect using a direct IP (xxx.xxx.xxx.xxx:4000), but not the computer name (DESKTOP:4000). What's strange is that this once (recently) worked , but now it doesn't, and the only thing that changed was a downgrade from ESET Smart Security to NOD32 (which means the Windows Firewall took over-- don't jump to conclusions quite yet).

OK, here's the setup:

Client-side:
Vista Laptop (Home Premium with TS hack-- ruled out as an issue)
ESET NOD32
Windows Firewall (port 3389 open)

Server-side:
XP Pro Desktop (specs in signature)
ESET NOD32
Windows Firewall (port 4000 open-- I changed the RDP port to 4000 in the registry as a security measure)

Both are connected through a WRT54G router. Port 4000 is successfully forwarded to the desktop IP (192...101). Both computers are on the same workgroup. File and printer sharing work just fine.

To attempt to fix this so far, this is what I've done:
--Disabled the Windows Firewall on both machines and then try it-- unsuccessful.
--Disabled the NOD32 protection on both-- nothing, with and without the firewall.
--Double-checked router and firewall settings-- everything's correct, which makes sense, given that none of these settings changed from when this once worked.

What's strange is what I attempt to "Browse..." for a computer from within the RD connection dialog from the laptop, and try to expand my workgroup, it gives me a message saying it cannot find any terminal servers.

I'm an A+ tech, but this has me stumped. I must be missing something. Any help would be greatly appreciated. Thanks!