Here's a rant from my experience:
85% of problems(viruses, slowdowns) can be avoided just by paying attention and being smart about what you're doing and what you're downloading from the internet. I haven't seen a virus on my XP box for at least 5 years and the performance is just fine. When clicking through the installation procedure of any program, take care to notice those sneaky checkboxes that install additional toolbars or programs that slow down the computer. Most antivirus applications and non-Windows firewalls also make the computer sluggish, but if you have problems with viruses, then you don't have much choice but to keep them enabled.
It's useful to look through the list of installed programs from the control panel. Anything you can't recognize can most likely be uninstalled. Unnecessary services can be disabled from the services panel(Start->Run->"services.msc") if you know what you're doing. Sometimes there's also useless stuff in the Startup folder that can be deleted(Start->All programs->Startup) and also the Startup key in the registry(can be accessed via "Start->Run->"msconfig"->Startup).
I like to completely reinstall Windows every 1-2 years to make it run at optimal speed. A nice trick is to use an nLited
installation disk as this will only install the things you need. I've even been able to install a vLited
Windows 7 on a netbook with a 4GB disk and it runs great for what it's meant to do.
If you want a responsive system, then keeping your hardware up-to-date is quite important. For me, this means having at least a Geforce 8 or equivalent GPU, two CPU cores and a modern harddrive.
Running under the Administrator account leaves a lot of backdoors open, but on XP a limited account is quite annoying to use. The vastly improved security model of NT6 (Vista and 7) does make things easier though. Currently this isn't a problem in the Linux community, because most Linux users know computers well and know the possible consequences of running under the root account and how to effectively switch between root and normal accounts. However, for those coming from a Windows background, it might be tempting to always use the root account for convenience, even though it's potentially more dangerous.
If you want to use Linux, then it's important to know a few things. Firstly, it's an OS made by developers for developers. A lot of things don't make sense to the casual users. For example, it's hard to get by for a long time without having to use the shell prompt to accomplish some task. Secondly, Linux comes in many variations(distributions). You might have to go through several distros before you find one that suits your needs the best. My favourites are Sabayon
, both of which I use for very different purposes(one as a desktop OS, the other as a lightweight server). Thirdly, hardware support is not quite there yet. For example, even though NVidia and ATI have started making relatively decent drivers for Linux, they're still not compatible with every distro. This has kept game developers from making any larger games for this platform.
Well, that's how I see it. I hope it helps!