I've got Samba running on my Slackware server. I have a connection setup for our laptops and my xp desktop. When I initially setup the connection through "map network drive" I put in the usual //SERVER/USERNAME (/ or \ I don't remember) and of course it shows up. I can access files, write, read, do everything. When I login the first time it asks if I would like to restore the connection on startup. I check on the box, but everytime I start up, it fails to reconnect. I have to manually click on the network connection under "my computer." A window pops up that says "incorrect password or unknown username for:" In the username field I see "/IP OF SERVER/USERNAME." When I retype in the password it reconnects and works fine. It gets annoying after the 10th time of restarting.

I was thinking it might be my wireless card. That perhaps it's trying to reestablish the network connection before my wireless card has actually connected to the router, but my brother's on a lan connection and the same thing happens to him.

The samba forum only gives one answer to this exact question. It says that I do not have the account setup on the server, but clearly I do. It's my main login for that machine and it's also my samba login. Clearly the account is present.

Set your Samba server up as the Master Browser ... (look into documentation for proper syntax/placement)
Also, look into the "OS Level" option.