best way to get next ID in database table

Hi Experts,
I want to save the data of a record to the database (which has many rows).  I will need to do this in a transaction.  I want to get what the next ID should be (without using auto-incrementing rows).  So I want some way of locking the table so that I can do the following:
- Lock the table
- Get the next logical ID I should use
- insert my rows
- unlock the table

Is there a way to do this without using database-specific calls?
I could do something like this:
while(true)  {
   while (lock table does not exist)  {
      create lock table
      query other table for max ID
      insert using MaxID + 1
      delete lock table
      return
   }
   sleep (2000)
}