A) Check that the smbd and nmbd services are running.
B) Check your filewall settings. Are Samba Server & client ports open. 137-139 & 445. The last one you might want to check if your windows machine is a XP or Windows 2000 machine. Otherwise 137-139 are sufficient. Port 445 is what would be used if you disabled netbios over IP support in your windows configuration. Ports 137 & 138 are used to listen to netbios broadcast messages.
C) Is the username and password the same on the Linux Box as on the Windows box. Be sure to run "smbpasswd" to add the username & password to samba's smbpasswd file.
Code:
sudo /usr/bin/smbpasswd -a <your_username>
<your_password>
Also, check if you have the Samba 3 by Example book ( in /usr/share/doc/samba-<version>/ or /usr/share/doc/packages/samba/) which may be supplied either by the samba or a samba-doc package. It may be in HTML, PostScript or PDF form.