Hi,
Your question is a bit tricky.
If you're thinking some pieces of hardware and turn your PC into a Mac, well like everybody said it here before me, you definitly can't. The fact there is an Intel ship in the new models doesn't change much : a mac is… a mac (= a pc with such a strong mac protection so you can't turn it into a regular PC).
Now, if you were thinking to replace the clunky windows by the all shinny new Os X leopard you may have some hope.
Some super geek team managed to install some hacked Os X on some PC and make them run like a Mac.
BUT ! But first, it's somehow not very legal. Next, you need a hell of experience to do it. Then your actual PC may be not strong enought to handle this hacked OS X.
And let say you managed to find this OS, download it and installed it, you will probably get bugs with your external printer and/or other devices. Final point, you won't be abble to update your system since Apple is working hard to block any developpement outside its control.
Soo… Bottom line : it's much easier to get a real mac.
There are not that expensive and come with a bunch of great softwares. Just don't buy the crappy MacBook Air.