Linux really is a good operating system. But really only recommended for power users. After that your troubles with linux could be alleviated by choosing the perfect right distro for you. Basically if you know how to build a computer and tweak any version of windows out the ass (aside from vista), then you are ready for the technical difficulties of linux. It's just that you may have gotten too used to the technical difficulties of windows so you may prefer those over the uncharted lands of linux difficulties which in retrospect are very similar to windows. I'd say keep treading along with linux and mess around with it on a different computer, separate partition, livecd, or the least preferable virtual pc. Experience increases through use and exposure in this case which will also result in more powerful abilities. And i really also don't know how power users can even really be power users if they only know how to use windows. After all, those who only use one kind of software will only know how to use that one kind of software (sadly enough it's true).
First thing for linux is don't use ubuntu. I have a 7600gt as well, i've had no problem getting it to work in gutsy, but once it works in gutsy with 3d hardware acceleration, it makes my nic for no apparent reason just not work. Ubuntu is sometimes good, never really still.
I'm pretty good at using linux, there's no problem i can't get over in it, but i'm a solidified distro hopper. I like messing around with the really cool distros all the time. The only good ones in my opinion is linux mint (unfortunately based on gutsy gibbon so you'll have the same problems with it as you had with straight up ubuntu...it's just that linux mint is ubuntu done properly in my opinion), mepis (great way to get a fast install of debian stable onto your system...if not that, it's an awesome livecd), and pclinuxos is the highest on my list.
Reasons why you should try pclinuxos?
Check out drakconf and how it makes configuring your system really easy and makes it work...it's also very user friendly.
It's fast, and i've found it to be pretty stable.
It's got good repositories.
It also is a livecd so you can try before you install.
Win2k is not a bad os at all. That's a piece of software microsoft made too good, and xp in general is a very good os, aside from product activation. Vista blows ass.
I would say a couple of reasons why kde4 was running slow for you is that it's not officially ready to be used at all yet aside from testing, and also other distributions are faster than others, the slowest i've seen was the latest version of mandriva.