Problem to setup a Print Pool

Hi,

I want to put two printer identic (HP LAserJet 4350) in a pool on a print server (W2K3). There is how I proceed:

Go in properties of printer1
Port Tab
Click Enable Pool Printer
Click the 2 ports of my two printers that I want in pool.
Click Apply, than OK

The only thing this do is printing the same document on printer1 AND printer2.

What I do wrong ?