Should Windows XP be able to do a SMB lookup on an Alias.
I have an XP machine that cannot find the files on \Alias but can find them on \host.
If I do a ping or nslookup it can resolve the Alias.
Your question isn't completely clear as to what the SMB target is. Given the error you report, I'm going to assume it's a Windows Server.
BTW - before I start answering, all the info I'm using in this answer I got from this forum post. It helped me a LOT when trying to do something similar a few months ago for a client.
There are more steps that are in the post if the server needs to be able to browse to itself by that alias, and if you get Kerberos errors, there are comments about how to fix that with SPN as well. But the above steps are all you need generically.
NOTE - if the SMB target is a domain controller, you will need to go through the rest of the steps in that forum post or it will fail miserably. If it's just another server you should be fine.