Best of luck

First, check whether what you've done matches this -

Right click -> Personalise -> Themes -> Browse

If yes, then it's probably Windows. Perhaps it's limited to certain formats, and doesn't let you use anything outside of its permitted range. Sorry, I'm not too knowledgeable about this.

But, I can tell you, after learning about optimizing computer performance, this is something you do not want to do. If you want to keep your computer performance the same way even after a few years of use, especially with a laptop, you'd want to minimise visual effects your computer use. Sure, it might look nice, but soon, when you're confronted with speed vs. looks, I'm pretty sure you'd resort to using your good old vista theme, and even that isn't too perforrmance friendly.

If you're interested in optimizing your computer's performance, you can follow the following step:

Start menu -> Control Panel -> Performance Information and Tools -> Adjust visual effects (on the side) -> Adjust for best performance

The skin sucks, but it saves up a whole load of RAM, which you'll come to appreciate in the years to come.

I'd also recommend you go through the sequence of the tasks in the performance information and tools panel on the side, you know, the disk defragmentor, disk cleanup and so on.

Of course, if you're an IT pro, you can use BIOS to tweak features here and there, but BE SURE TO KNOW WHAT YOU'RE DOING BEFORE YOU DO THAT. Tried it once. Disastrous. Lucky I kept a log of what I changed or else I don't know what I could have done to my poor laptop. One change can cause a Dominoes effect to a whole bunch of other features. You'd want to have an IT pro beside you telling you what you should do, preferably someone you trust as well.

Hope this helps!

Hope that helps.