URGENT - concerning file sharing on Windows network

[-N-]

I have file sharing enabled on my computer, but whenever someone tries to access my shared files they can't. In fact, they can't even access my computer at all. (I'm running XP Pro, SP1, everytime I try to upgrade to SP2 my computer vomits.) The message that results is

[q]\\192.168.1.101 is not accessible

Logon failure: the user has not been granted the requested logon type at this computer.[/q]

How do I grant such a "requested logon type"? I haven't had a problem like this before, and now no one can access my shared folders.

edit: I tinkered around a bit in the Local Security Settings panel, and added "Everyone" to "Access this computer from the network", and now the error message is

[q]\\192.168.1.101 is not accessible

Access is denied.[/q]