Frustrated with Ad-Hoc, please help!

Hi
I've spent the last two days tearing my hair out trying to set up an ad hoc network for file sharing - not even ics! Just file sharing. First the setup:
Laptop A is my main computer, it's a Dell with an internal wireless card, it's a fairly new machine and hosts most of the files I want to share, it runs XP home ed. Laptop B is an old craptop I want to use as a media wall box, it uses a USB thumbdrive wireless adaptor and runs XP pro (just about).

I've gotten an ad hoc unsecured network set up - eventually. Both computers confirm they are connected with signal strength etc displayed, and both show the network with a blue circle in the network connections page. Now, I used the network setup wizard to assign them both to the same workgroup, they are on the same IP range (192.168.1.4 and 5) and subnet mask (255.255.255.0) but can't ping each other and can't share files or anything else. Simple file sharing is turned on on XP pro. I get the error message "Network name is not accessable, You might not have permission to use this network resource. Contact the admin to find out..." and "the list of servers for this workgroup is not currently available"

I've tried everything, I even followed a thread about the 'list of servers' message and tried getting into the registry stuff, but i need help badly. Thanks for any help!

Robbie