I haven't played in about 10 years and don't remember this feature, but someone on the GTA IV board said you could.
Is this correct? My PS2 hasn't played PS1 games for many years now (or DVD's, for that matter), so I can not pop it in and check myself. Thinking about those good old days sure brings back great memories though.
Ah, to be young again.
--- Now playin': Poker, GTA IV, WWE 2010, Borderlands, Fallout 3