Just about anything is possible, the question is what is involved in doing it. I will tell you that using anything other than the calendar's own forms to add data will likely be very difficult to accomplish.
For displaying of only one user's entries at a time, you could look into the 'Meta Calendar' or 'Private Events' plug-ins or the link to "Different categories idea" forum message in the 'Links' section of the Unofficial CalendarScript - Mods and Plugins site.
For a simplified data entry form, you could look at the "OneClick Event Entry" plug-in.
Dan O.
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