Rosetta is the application layer that allows for Power PC-based OSX software apps to run on the Intel Mac. Those apps *may* run a bit slower on the Intel mac as the Rosetta software is a translation layer between the PPC based progam and the OS itself.
Crossover lets a limited amount of Windows (Win32) apps run on top of the Mac (or Linux). Neat stuff. But can be tricky.
Parallels or VMWare Fusion (I vote for VMWare fusion) lets you run a complete Windows installation, in a window, from within the Mac. Pretty much guaranteeing the Win32 application(s) you need to run, will run without having to reboot the computer just to run them.
Boot Camp is essentialy a disk repartitioning tool kit that shrinks your OSX partition down to a reasonable size, then allows you to run Windows natively (on the bare metal) in it's own partition of the hard drive. The problem is that you have to reboot in & out of OSX everytime you want to do something Windows related. While this is great for games, it's a pain to reboot so often.
After using both these products, I strongly suggest VM Fusion. Parallels 3 has a NASTY habit of chewing up virtual disk files. Moved to VM Fusion and it's been rock solid. A friend of mine has a MacBook and had Parallels on it. He ran 4 instances of Linux on it at the same time. Problem is, Parallels not only ruined the 4 virtual disks for all the Linux installations, it hosed the entire partition table for the hard disk. He bought VM Fusion and tossed his copy of Parallels.
The only caveat I see with VM Fusion is using USB devices on the virtual machine as I've seen BSOD's on the VM with these. Hopefully VMWare will iron this out in short order. Good thing to note is that even with many BSOD's on the VM, there was no file corruption of the VM itself.
Good luck!