VMWare works really well, although I have not tried Mac OS or OS X on it. But, I tried Windows XP and Ubuntu Linux 8.04, and they both worked fine. I suggest that if you choose to try VMWare though, that you have very good specs for your machine. You'll want a lot of RAM and a powerful CPU. Let me give an example.
I'm using Windows 7, which uses a lot of RAM (less than Vista, but still a lot more than XP). It needs at least 1GB to run solidly (which unfortunately, because I got my laptop in March '06, it only HAS 1GB of RAM at the moment), but other systems will need to share it's RAM.
For example, when using XP, you should have at least 512MB for it to work smoothly. But running XP through VMWare means using 512MB of RAM, leaving 7 with only 512MB RAM, meaning because 7 is hosting VMWare and powering it, your whole computer is going to lag. Now, if I had 2GB RAM on 7 and used only 512MB on XP, my computer would handle the load a lot better. Also, CPU power helps it. I recommend at the VERY least, 2GHz, probably 2.6GHz, and if possible, at least two cores. I have a dual-core processor, both with 1.73GHz each. It's not very good. It could be worse though.
But if your computer isn't going to be able to handle it, you might want to look into Hackintosh. I can't say how or even if it works (it should do, but I don't know how well), plus it's pretty much illegal, but it's more than likely your best bet. I honestly don't know how good it is compared to a normal Mac machine though.
