Before Outlook 2007 came out, there was only one Open Source project that really allowed you connect your Google Calendar to sync with Outlook 2003. It was called Remote Calendar. Even then, it still had its issues if you did't have the newest version of .Net and other Office patches. The project has progressed since then and can be found at: http://sourceforge.net/projects/remotecalendars/
With the introduction of Outlook 2007 it is easier to sync your Google Calendar in Outlook and layer it with other calendars you may have. Check out
http://office.microsoft.com/en-us/outlook/HA101674951033.aspx?pid=CH100776881033
I'm a big Outlook user at work. And once upon a time I used to be for at home as well. That was one of the reasons I went on the search for an Outlook google calendar sync option. However, I found that when I started using multiple computers it got to be such a hassle to make sure my Outlook data was correctly working with the Google calendar from my "primary" machine. I opted to just "display" my google calendar in my Outlook *if* I used it and opt to view the Google calendar through its web, email reminder, and SMS options. Overall, I took the other route...used Outlook to move all my other calendars into Google. In the end I found that since I couldn't bring Outlook with me to all my machines, that I should only use Outlook to take my info to google where all the info could be together.
If you are wanting to keep all your calendar information on one machine in Outlook, then Remote Calendars will work well for you in Outlook 2003. The built-in functionality in Outlook 2007 should also work well for you.