Yes, it can be done, though it's not really the way the routers are designed to work.
Assuming the laptop had built in wireless, all you'll need is a wireless router with built in Ethernet ports. You'll have to set up internet connection sharing on the desktop, and make sure both the desktop and the laptop are in the same workgroup. Then, both computers can use the dialup connection.
You think ONE computer is slow on dialup, just wait until you try to share it
This is how we had out internet connection set up 5 or 6 years ago, before we got highspeed.
If you need more detail, let me know.
