there were a few products for connecting a pre-X Mac to a windows share, but they seem to be discontinued.
Easiest way is to use a USB memory stick to transfer the files, if both machines have USB. Or just email the files if they are small.
If not, the best bet is to use web-sharing. turn on personal web-sharing on the Mac (cant remember how, search the Help), move the files to the web share and then point your PC web browser at the Mac's IP address. click to download the files you want. that covers Mac -> PC transfer.
you can do the same for PC -> Mac, but I've never set up web sharing on windows so not sure how to do it.