Recently I've come across the task of modding a common Windows XP to look and feel more like a MacOS Tiger. I've stepped up to the challenge, and there's lots of good software to help you. After giving them all a try, I find the following the most usefull:
- StyleXP - with this one you'll get the bar and windows just like a mac (look for styles in wincustomize!)
- ObjectDock - Rocketlaunch is also cute, but objectdock is more versatile.
- Launchy - Remember quicksilver? this is close :)
- Topdesk - this is a good expose!
As for the dashboard, the only widget tool I'm familiar with is google desktop. so you're probably good with it, too, if you have a reasonably decent machine (RAM-wise).