Do you have Outlook or Outlook Express? In Outlook, you can use the calendar feature, I don't think Outlook Express has it though (but it's been a long time since I've had a reason to look). I don't know why you'd need a hotmail account for it? If you only want the reminders to pop up on your computer, you don't need to give it an email address at all, but if you want email notifications (only really useful if you carry about some sort of PDA that can notify you when you get a new email...but then, if you had a PDA, you would already use that for your appointments, right?) then you should be able to send those to any email account.
You can also use some free, online calendars, and then those you would want to set to send you email notifications if you need reminders, since you can't get them to pop reminders up on your desktop. The advantage to those is you can check your calendar from any computer, not just the one you have your Outlook calendar saved on. Yahoo calendars seem to be reliable.
There are a few drawbacks to using a calendar on your computer. You can't refer to it when you're away from your computer! For me, this limits its usefulness. It does me no good to walk into my office after being in the lab or on the farm for hours to find a reminder on my screen for the appointment I missed two hours ago. This is where PDAs are more useful if you need something to beep at you to remind you of an appointment while you're away from your computer. Another drawback is that you don't have the calendar with you when someone is asking about scheduling stuff, so you either risk double-booking, or you forget to enter it in the computer when you get back. Again, a PDA or paper pocket calendar are more useful for this. The last problem I've had using calendars on the computer is trying to decide when to set the reminder. When you're relying on it to beep at you instead of getting in the habit of checking it every morning for the day's appointments, it's not very helpful if it notifies you of an appointment 5 or 15 min ahead, and you need a half hour to finish up something else you're in the middle of when the reminder shows up. Likewise, if I have a meeting early in the morning, or on the weekend, I usually set my reminder for 1 day ahead so I remember to get in early the next day or at all. But, by the time I get home, I don't always continue to remember it! I end up setting multiple reminders on those really important, can't miss type meetings, which in every software I've used, requires duplicating the appointment. I haven't come across one that will send a reminder multiple times for the same appointment, other than as a "snooze" type setting, which isn't what I want. I want something that will remind me the day before, the night before, and the morning of (even better, if it could zap that information to my alarm clock to wake me up in time to get ready for the meeting, that would be the ideal thing).
I really was more organized when I was in the habit of carrying a small pocket calendar. The problem is that I just can't find one I like anymore.

There used to be so many choices for those, but now that everyone has PDAs, I just can't find a paper calendar in the size and style that would keep me organized.