Yes, you're correct. To make a PLU with a fixed (preset) price you need to set the PLU status value appropriately. In particular digit 8 of the status value determines whether a PLU is open or preset. The status value is a decimal (octal, actually, sort of) representation of a bit mask; note the use of the values 1, 2 and 4.
For example, to make a PLU non taxable with a preset price, you would use a status value of 00000001000000. Note that when entering status values you can leave off any leading zeros. For the previous value you could just enter 1000000. The value of a particular digit is the sum of the desired values for that digit. For example, to make a PLU preset but also disable the Promo feature for that PLU you would use a 5 for digit 8 --- 1 (for preset price) + 4 (to disable promo) = 5.
Hope this helps ...
Steve, November 2009