Here's my checklist for getting file sharing to work on WinXP:
-Check that you have TCP/IP, Microsoft network client and Microsoft file sharing enabled on both PC's network config.
-Assign IP addresses in the same subnet; 192.168.1.x/255.255.255.0 is recommended for this, but other ranges will work.
-Use the same username and password on both computers (you HAVE to set a password, unless you want to edit the security policies; you can then use tweakUI to auto-login if the password really bothers you)
-Run the network config wizard in the Control Panel. Since the point is not sharing the internet connection, just getting filesharing to work, choose only that. No need for a config floppy either.
-If you are accustomed to the way sharing worked in previous windows versions, disabling the simple file sharing in the folder options might make you more comfortable.
-Share the necessary folders and set permissions (on both the folder AND the share itself) to allow full access to your username or even everyone.
-If you get timeouts, you may need to disable the firewall on the PC you were trying to access. If you are directly connected to the internet or on a router's DMZ, careful: disconnect before disabling the firewall.
I think that's it, off the top of my head.
Excuse me if some things are not properly worded, I'm used to giving this sort of advice in Portuguese, so some terms could be different.
Hope this helps.