I've been lurking around for awhile trying to find a fix for player_a.dat error while running GTA 1 in dosbox in 3dfx mode.
Finally i've found a solution.Am not sure if anyone has posted this.
1) Download Dosbox (ykhwong)
2) Install Dosbox and install GTA using Dosbox
3) Run Dosbox and execute GTA.bat in dosbox, within the GTA Folder.
NOTE: Avoid Running GTAfx.exe
Can't really explain much here, so i decided to create a Video tutorial in Youtube in detail, explaining how to do it.
If you are interested, do check it out.