PC to MAC connection problems

On my G4 running OS10.4 I can get a shared connection to my PC running XP - no problem. It's the other direction that's giving me nightmares.
On the MAC side:
I've enabled file sharing
I've enabled windows sharing
If I click windows sharing it tells me I can access from a windows pc at 192.168.0.3\myshortname.
I have firewall turned off

On the PC side:
I've gone through the wizard to create a new connection which appears on My Network Places as "macg4"
I have firewall turned off.
Clicking on macg4 gives a username/password window
For username I type 192.168.0.3\myshortname and then give my password.

I get the message "192.168.0.3\admin is not accessible. You may not have permission....." etc.

So what's with this "admin" that's suddenly appeared?
Any help will be greatly appreciated.