Ahh, alrighty then
WindowsXP HOME has NO support for logging into a network, whereas WindowsXP Pro DOES. This is not to say that XP home can't get on the Internet or transfer files across the LAN, but some major things were left out of the Home version (as far as it's networking capabilities go.) I can't say for sure if this is what's causing the problem you're experiencing, but I'd be willing to bet that if you had XP Pro on Machine A, you wouldn't be receiving those errors.
I just thought of a long way around this that might work for you. I've never tested this specific solution, as I don't have any XP boxes (all mine are either FreeBSD or Linux, with one Win2k box for my games
OK, here goes:
On Machine A, share out a test directory.
On Machine B, map a drive to the test share on Machine A, then share that drive and see if you can see the contents from your Linux system. I have NO IDEA whether this will work or not, but it's worth a try...