06-10-2008,05:54 AM
First to know. Original DVDs must be swapped to burned DVDs. Original CDs, must be swapped to burned CDs.
Does your Demo-Disc has a Menu to select between multiple demos from one disc?
Please post dir+filestructure (and also, which media (-> cd or dvd) it uses).
This way, I could help ya better.
1. Create an ISO-Image of your Swap-Disc.
2. Modify the ISO and change one ELF, that is startet after swap (after swap selct the Demo, you want to "play" and your Homebrew should start).
ELFs, that are started after swapping:
-Start-ELFs from Demo-Discs.
(CDVD boot up and shows a Menu, where every Picture, where you can start a demo, which is linked to an ELF-File. This ELFs can be replaced.)
-Should be the same with NetConfig, but I'm not sure about that.
It's really long time ago, this method was used, to boot Homebrew.
Try to search :google: for "FIFA Demo PS2 Swap", or something similar.
3. Burn the new ISO.
4. Insert Original Demo-Disc, or Game.
5. Use the Swap(-Knife)-Method.
6. Start "the Demo" which ELF you modified, or Netconfig if you've replaced original-netcnf with your ELF.
7. Your Homebrew should start (i.e. uLE, SMS, FMCB-Installer,...)
Btw.: GT3 A-Spec has a Netconfig for LAN afaik.
Should work also and I could test it here, because I have this game also. 
Edit: 5Second Net-Research gives me this on ps2dev.org. 
http://ps2dev.org/ps2/Tutorials/TUTO...Demo_Disk_Swap
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony BBA
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
MAX/Datel 32MB&64MB
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux