@ nicolasraage
hey there, im having the same trouble...
see what i wanted to do was back up the gta3 cd's, after i copied and pasted the files to my hard drive i was able to write them to cd just fine too. when i tested the cd's i found that the play cd wasnt recognised and it wanted the real one. truth is its not the play cd thats the problem, its the install cd. see when you install the game it copies a file called gta3.exe to your hard drive, this is the exe file that starts gta3. what i wanted was to fix the gta3.exe file on cd so that when i installed it the game would automatically work on my hard drive.
the gta3.exe file is located in the data2.cab file on the install cd. you need a file called i6comp to change the file, but then you need to change a file called data1.hdr so that it will install afterwards. i havent found out how to do this yet.
click here and download this fixed gta3.exe file, when you have done that, find the gta3 folder on your hard drive and replace the gta3.exe file with the version youve just downloaded. the game will work then with the play cd.
click here