Can't blame you for having an opinion about the looks. I too think that linux looks quite ugly with the default themes that most distros ship with.
However, on the technical side of things, Linux has a way more advanced gui than windows XP, and it's quite on par with Windows Vista and getting closer to OSX

That means that if you want transluctanct windows, 3-dimensional desktops, shadows on your windows or a combination of such things. Then it's definatly possible under linux -provided you have an OpenGL capable card (I think Geforce2 and above will suffice!).
What you might be forgetting though is that as with so many other things Linux-related. There's a huge list of choices so I'd suggest looking in freshmeat.net for themes or at sites such as gnome-look.org and kde-look.org.
If you take your time, you'll be able to make Linux really simplistic and nice to look at, or brimming with desktop candy

Don't forget to spice up that desktop with widgets (you can use the OSX widgets somehow!) offered by programs such as Karamba and gDesklets

Some examples:
Vista-like look (transparent windows and shadows displayed)A green desk with an OSX top menu bar and a dockerMany more can be found by going to either kde-look.org or gnome-look.org unchecking the box "Don't show screenshots" in the filter box in the righthand pane, clicking apply and entering the screenshots section

Granted, it requires some effort, but you can totally smoke the windows-boxes --best of all, there's so many many styles to choose from. So if it's a black matrix-like hackers theme you're going after, that'll be there too