Iv never tried to do what your trying to do, Iv only done this after connecting to a NT based server, then its just the matter of properly adjusting the proxy settings in IE..... so until someone who has actually attempted to do this comes along...Ill try to guide you.....though we may walk into a tree from time to time
First thing should be :crosses fingers: to make sure both computers are using the same IP settings, make sure that your laptops IP address is similar to your desktops address. Ie if your desktops address is 10.0.0.1 (for example) make sure that your laptops address is something like 10.0.0.2
You make your laptops connections IP address anything you want do the following: (on your laptop) Goto Network Connections > Right click your Dial Up to your desktop > Select Properties > Select the Networking Tab > Double Click on the TCP/IP selection, select the box that say "Use the Following IP address" and enter the one you want, also check the advanced tab and make sure that XP's firewall is off.
Then dial into your Desktop,
Once your connected to your desktop system go into command prompt and type "ipconfig" it will give you the address of your Dial Up connection: it should be the IP address you entered and the subnet should be 255.255.0.0, if it is you can close the windows...if not close the window anyway and post back what it said.
Now try going accessing your desktop system from your laptop by clicking on my network places > and in the address bar type \\<your desktops network name> and see if it brings up a list of your desktops shared resources.
Post back and let me know..