If you are using the method of logging into both accounts at the same time, you could do the following.
1. Create a new empty calendar from the iCal file menu, select which account you want to create it in.
2. If you have only a few appointments you can move them individually by editing them and changing the calendar in the edit options.
3. Alternatively you can copy all the appointments in one calendar to another and delete the original.
4. To copy a calendar ctrl-click on it from the menu that appears when you select the calendar button (top left corner of iCal) and choose export (export it to your desktop for ease)
5. Double click the exported file and choose the new empty calendar to import them into.
6. Ctrl-click on the original calendar from the menu that appears when you select the calendar button and choose delete.
Thanks for that. Unfortunitly I dont think I gave you the right info on waht I am trying to do. I want to import all my Ical appointments (of which I have many) into another Icloud account. At the moment when you sign out of Icloud it wipes all of my appointments so I loose everything. I wish to load all this into the new Icloud account so I loose nothing. It is simple for the bookmarks and the address book but I have problems with Ical.