start a single player race, on the track selection hold CTRL and you should see an X and Y option next to the tracks, click one of these and you will get an open config track.
There are a fair few s1 hosts, the trouble is they are mostly empty (see pic of lfsworld - racers/hosts online.) and a lot of people filter out empty servers. If you join an empty one that is running your preferred combo you may get some others come and join you.
If you are waiting for S3 then why not buy S2 now as you will have to buy it to get S3, if you are looking into league racing then as you have probably noticed its nearly all s2 leagues. Plus they are a few more populated public servers.
Afaik Vob's just change the physical appearance of the car and have no affect on the actual handling/physics of the car. The problem with .vob mods is that while the .vob does change the appearance of the car, LFS still uses the original unedited car model for collision detection which causes problems when racing against others due to the differences in the original car shape and the new modified one.
They used to work online (z28 and before) but in the recent test patches they are now detected and will give people using them a JOOS: CAR error when they connect to a server.
Thanks for pointing it out, but I get the same thing as Deko. Tried using it on the dfgt and just get "The code you entered is invalid. Be sure you typed the code correctly and try again." which was copy/pasted direct from the voucher code page
As NotAnIllusion mentioned, even tho you are now s2 you can still see and join the s1 and demo servers, these servers are restricted to the licence limits.
When you bring up the server list (multiplayer>dislpay list of hosts) you can see what cars the server has enabled by the dots in each cars column (hope that makes sense)