MarcoM and I did some races and exchanged cars via the Adhoc Party online PS3 program. It took some effort to get things to work, but we came to the following conclusions:
1. Download and install Adhoc Party on your PS3. You will need a japanese account to be able to do this. (toturials on how to install a japanese account and how to download and install AHP have been posted before).
2. Register your PSP with your PS3, using the same account as you use on your PS3 (this doesn't have to be the japanese account). If you have another account on your PSP, delete it first and than register the PSP with your PS3.
3. Hard wire your PS3 to the internet, so do not use Wifi. If you start Adhoc Party while not connected with a cable, it will tell you so.
4. Now you are ready to play. Start AHP on the PS3 and select the top option (press circle, this is accept in Japan, like most of us would use x). The first time you do this, it will take through a number of screens (all in japanese and probably about excepting codes of conduct and the like). Just keep pressing O to accept (maybe in one or two screens you first have to select the other option).
5. This brings you to a field with a large circle, showing a world's name (e.g. A).
6. Step to World J where all our GT friends should be (use the shoulder button L1 to step left for quick access, or R1 to visit all the other worlds).
7. Again a big circle, with numbers 01 to 64. GT games (or rather GT Planet) are to be found in lobbies 30 - 35. Use the left analogue stick to highlight one of these lobbies and while holding this room number, press O.
8. This will show 3 lobbies. With the analogue stick (or up/down buttons) select the one you want and press O again.
9. Now you are in a big green playground. If you are lucky, there is a little house showing with a name like GT or GT Planet. With the left analogue stick bring up a circilar pointer and move it to this room. Press O again to enter the room. If you get a dialogue with 2 options, select the bottom one, and press O.
10. No one there? Move your cursor to some emtpy spot and press O, and O again. Fill in a name for your room (e.g. GTPlanet rules!), highlight the bottom left option, and press O. Now you have opened your own room.
11. You are now in a game room. Here you can chat by keyboard or head set, and also join games. Time to fire up the PSP.
12. On your PSP, go to Adhoc Mode and select multi player.
13. Pick a room (x), and create one (unless one is already available, just join that one). And you are ready to race.
14. For trading cars, just select share and trade and be patient for your friend's cars to show up.
Edit> As far as I know, you need to be from the same region (NTCS, PAL) to be able to trade with each other.
Edit 2> There is a way to scan for rooms already hosting GT PSP. Follow the instructions in
this video.
