There's lots of things that you can do on the internet that can compromise your safety. It's best to think very carefully about this before you start playing around. Be careful how you interact with people and services, and have little trust in things (always do your own scans for viruses, be suspicious about advice to drop any precautions, don't put much faith in other people's assertions, etc.).
There's an awful lot of malicious and weird people on the internet, some of them spending a lot of effort into making complete pests of themselves (to put it mildly). You need to be prepared to deal with it. There's not a lot that you can do about much of it, but if it's not a complete surprise to you you'll be better prepared.
Avoid using personally identifying information with anything that you don't know, with absolute certainty, what'll be done with the information. That means full names, phone numbers, residential addresses, etc. If someone or something asks for it, think about why, and whether you really need to provide it (perhaps you can provide false information, limited information, or not bother to provide any details), and think about whether you'd be best looking somewhere else that doesn't ask you to provide such details.
I flagrantly break that philosophy, with my full contact details listed publicly on my website and a few other places. But I use the internet for business purposes, and I already have my details listed in both the personal and business telephone directories. Trying to run a business doesn't work if you're hiding. Though I avoid giving out my details to anything that asks for them, as much as possible.
Don't be paranoid about it, though. Not providing correct details for something you buy will mean you won't be able to make warranty claims, or ask for help about it. And it is possible to safely use a credit card on the internet, you just have to be sensible about it (only using encrypted connections—which means, amongst other things, not in writing the details in e-mails unless the message is encrypted—most aren't).
You have to consider what they might do with the information. Giving your personal details to a stranger has all the obvious risks (stalking, obscene phone calls and mail, etc.). Giving them to a business has the risks of being deluged with advertising, requests to fill in surveys, and so on, from them and any other business that they sell your information to.
You can do yourself a big favour and stop using software that are problematic in themselves. In particular Microsoft “Windows”, “Internet Explorer” and “Outlook Express”, are the worst of the lot for exposing you to risk (allowing malicious software and users to do things to your computer with little restriction, if any). There are plenty of alternatives, but if you can't rid yourself of Windows, you can at least stop using Internet Explorer and Outlook Express, they're easy enough to find alternatives for.
Think about this if you consider it too hard to learn to use something other than Windows: If you can learn to cope with all the weird requirements Windows imposes on you to get a job done, and put up with all the malarkey involved with keeping Windows running, you're just as capable of learning the sensible requirements that alternative systems will demand of you.