It’s not that it’s “that hard”, it just takes some background knowledge. There isn’t an easy editor for the themes or anything like that, to do your own you essentially have to create or edit a couple dozen files in a cohesive way.
Just jumping into it without knowing the background would be a little like learning Spanish by reading Spanish poetry. Spanish isn’t necessarily a difficult language, but it’s tough to go from zero knowledge to catching the nuances quickly. Same way with the two languages you need to learn to make a successful theme. (calling HTML/CSS one combined)
Which isn’t to say you can’t do it, and I’d be happy to try to help as well. (maybe I can try to make it work in IE when johnpowell is done ;)
There are probably a thousand existing themes for wordpress though, many on wordpress.org and many others in various sites on the internet. It may be easier to find something you like the general feel of and then make small tweaks to make it your own. A change of background images and a few colors can make something seem quite different and may be a better way to go.
Good luck with it and drop us a link when you get going.