We have several guides for transferring files right here on this forum, but I'll admit, they're not easy to find as they're buried in threads just like these where people ask for help rather than serve as FAQs (hmm, this gives me an idea).
Anyway, your best bet would be to do an Erase and Install of Leopard onto your new Mac before anything else. Networking with Windows is far easier on Leopard than on Tiger. Once you upgrade, your Mac should detect machines on your network and you should be able to connect to them automatically.
However, if you really want to stick with Tiger, follow these directions:
First you connect your Mac and PC with an Ethernet cable. Then click on the Start button, hit Run, and when the little box pops up, type in "cmd" without the quotes. Then the command prompt should open (it's a black window). Type in "ipconfig" again without the quotes. You'll see your IP address (an example of what it looks like is 127.0.0.1).
Now that you have your PC's IP address, go back to your Mac. Close all programs. At the top, click on Go and then at the bottom, click on Connect to Server. A small window should pop up. In the little area where it says Server Address, type in the following:
smb://xxx.xxx.xxx.xxx
Replace the x's with the IP address of your PC. Hit the Connect button. Wait a minute for the Mac to connect. Another window will pop up asking for login information. You can just leave this blank and another window will pop up asking which folder on your PC to access.
Usually you'll only see the Shared Documents folder, but you can enable file sharing on another folder/drive on your PC so you can access it from the Mac. If you need directions on how to share files on Windows, post here and we'll help you out.
You don't need to setup servers or do anything ridiculously complex just to transfer files, just follow some simple directions.
You can check out
Apple's guide to transferring files if the above doesn't work for you, though I think it's been updated to reflect Leopard.