We we're trying to connect to a Mac running OS X 10.5.1 from a Windows machine running XP over the network...
Following the instructions the Sharing Preference on our Mac gave us, we were without a chance.

OS X 10.5. suggests the following path: smb://10.0.1.9. - we got nothing but error messages on our Windows machine. I remembered in OS X 10.4. it used to be backslash, - and indeed, without the "smb" and using double-backslash instead of double-slash it works.

To avoid problems with routers blocking your connection, use a network (ethernet) cable to connect your mac and your PC directly.
- Switch off the AirPort on your MAC, for this will give you the wrong address in the Windows Sharing pane.

Why the hell do Apple tell us "Windows users can access your computer at smb://10.0.1.9." when this obviously doesn't work? Maybe I don't know enough about Windows (true!) and using this path somewhere other than in Run from Start Menu would work..?

However, the Sharing Preference Interface in OS X has gone from bad in 10.4 to worse in 10.5 - this is not what a Mac should be - which is to offer an intuitive and user friendly interface. Although it must be said, technically it has improved, for example by offering the long missed option to allow access to specific folders.

On Windows enter your Mac's address 10.0.1.7. in the Run app:

If you can't see the smb://... path in your Mac's Sharing Preference, remember to click "options" located bottom right in the sharing preferences window and select "Share files and folders using SMB" and deselect the AFP checkbox - this used to simply be "Windows Sharing" in 10.4 Tiger...

To configure your Mac so you can access more than just your shared folders from the PC, add whichever directory / folder you want by clicking on the plus below the Shared Folders pane in the Sharing Preference window (in my example this is the folder "Larne" - with you it might be the "Documents" folder. Then grant Read & Write access for yourself in the Users pane.

Troubleshooting: If you still can't connect, try...
- with your firewall on your Mac turned off (remember to turn it back on when you're done).
- try using a direct computer to computer ethernet cable connection instead of going through your wireless network.
- If you have a direct connection with a cable, make sure to turn off the AirPort on your MAC!

A new feature in Leopard is the inclusion of an application called "Screen Sharing" - it is apparently based on Apples Remote Desktop. The Screen Sharing app (which Apple suggests we use via the iChat app where it is built in as a feature), is actually a separate application located in
/System/Library/CoreServices/Screen Sharing.app

Mac OS X Hints posted the following hint, which greatly improves usability of this app, by adding favourites and the Bonjour-Browser, - enter the following command in Terminal:

defaults write com.apple.ScreenSharing ShowBonjourBrowser_Debug 1

Apparently some people have problems sending files from their phones to their Mac under Leopard. There's a new item in the System Preferences under "Sharing" called "Bluetooth Sharing". This must be activated to accept files sent from phones.

My Apple, this is not so impressive... (From Heise Security) via MacRumors.com:
Leopard's firewall] is not activated by default and, even when activated, it does not behave as expected. Network connections to non-authorised services can still be established and even under the most restrictive setting, "Block all incoming connections," it allows access to system services from the internet.
Read on..