I am totally new to my blackberry and was given a 7230 that has a very large contact list already on it. I need to get rid of this contact list on the BB then sync with my computer to add my contacts.

How does one go about deleting multiple contacts?

I forget how but it's done with desktop manager. Look around in there...

Open Desktop Manager
Open Backup / Restore
Let it read the BB databases
Find "Address Book" on the BB and clear it

That should do it.

a security wipe would be more effective and would erase all of the previous users data!

I tried doing what you said to do to clear my address book but the address book is greyed out and the clear option is not available? Any suggestions?