Sure, basically connect the Mac via USB as normal and then click on the iPod on your sources list (the column on the left). In the window you will now see a Summary page and what you want to do is click on the 'Restore' button. Heads up, it will wipe your iPod and reformat it for the Mac, but you'll loose anything currently saved on the iPod (iPod only, not the music saved on the computer).
Sure, if you bought a new iPod you'd be able to get the music on it, but its not nessssary so don't waste the money - unless you want a new iPod of course! Music files are music files, they are interchangeable - MP3, AAC etc work on both Mac OS X and Windows XP/Vista exactly the same. There are a few formats, like WMA/FLAC that iTunes will not play, but since you used iTunes on a Windows computer you don't have to worry about that as iTunes on a Mac or Windows saves to the same formats.
As you've correctly guessed, your only real trouble is that your iPod is associated with another computer (iPod's can only be associated with one computer, so that we can't trade GB's of files easily thanks to the music industry) and its easy to get round this, just restore the iPod and it will work with your new computer, a Mac in this case.
let me know if you have any questions or if I didn't explain something very well.