I can't talk about 10.5.8 but on more recent Mac OS versions there is an extra unexpected step to allowing access to shared Mac folders from some windows OSs. I'm assuming the same 'gotcha' and equivalent settings exist on older Mac OSs.
In System Preferences / Sharing you will already have turned on "File Sharing" and set up your share folder and their permissions.
The extra trick is, On the Sharing settings page, with "File Sharing" highlighted, Click the "Options..." button.
In there you need to ensure that "Share files and folders using SMB" is ticked (it almost certainly is already), and additionally you need to tick each mac user account that you need to be able to be authenticate as from Windows. When you do that, you need to present the user's Mac password for each account again (as the Mac needs to keep a copy of the password in a 'less secure' form than it would usually store the password).
The connection from the Window system is authenticated against that extra copy pf the Mac account password. Without individually enabling the Mac user accounts in that way, you will not be able to authenticate form Windows.