URGENT - concerning file sharing on Windows network

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]

The easiest way is to make an account on both machines that share the same username and password.

Is the guest account enabled?

Guest account is enabled.

Creating a user account with the same name and password is infeasible, as I am on a fairly large network and giving out my name and password to people who want to access my shared documents seems unwise.

Domain or workgroup?

If you are on a workgroup, make sure you run the network setup wizard as it magically enables the "make the network work" feature that Microsoft hides and leaves disabled by default.*

(* Not really, but the network setup wizard does make getting the network working a lot easier)

I get a user and password box when I try to connect to another computer on the network using workgroup.

That depends on the other computer of course. And in that case you have to do what you said earlier (create a similar user and group on the local machine)

Oh, and it would be best to leave the guest account off, for security reasons, seeing that you are on a reasonably-sized network.

I'd remove Everyone accessing it from the network, and remove Guest from Deny accessing from the network, and make sure unknown users authenticate as guests in the network connection's properties :p I'd also make sure all my shares are read-only to guests, especially if you're on such a network, otherwise you can get infected rather easily :p