Wireless networking hell

[Ghoulish Delight]

AAAARGH!

New laptop. Everthing's great, but I'm having SERIOUS issue with networking.

Here's the summary:

I'm trying to file share between our desktop (connected via a wire to the router) and the laptop (connected via wireless). I can't even ping between them. Neither by name nor IP. Pinging by name fails to even resolve an IP.

However here's what does work. The laptop has internet access on the wireless network. If I plug the laptop into the router via a cable. Also, from the laptop (when on wireless), I can ping any other wireless device, but no wired devices.

The desktop can ping all other devices, wired and wireless, but can't ping the laptop.

I've already disabled all firewalls, checked every god damned file and network sharing setting in the universe. All seems right. And this setup worked fine in the past with the same router (but different desktop and laptop).

Here are my 3 guesses:

1) Problem with router settings. I find this unlikely because it used to work with the old computers, and the desktop can talk just fine with the other wireless devices on the router

2) Problem with the wireless adapter itself. This seems most likely to me, something that the wireless adapter is doing is preventing the router from moving packets from wireless to wired and vice versa (although it can get out to the internet via a wire, so that seems odd)

3) Out of date router. This is an old router, purchased when Wireless-N was brand spanking new (so new it wasn't even officially a protocol yet). It could be that this brand new laptop is using technology that the router has no idea what to do with.

I'm really hoping it's #3, but wouldn't mind if someone happens to be able to think of anything else I can try.