if your trying to unlock everything then start by building up a heap load of cash...
go to beginner legue and then to turbo cup, then race on 1 of them. if you win then you get 5,000 credits. if your 2nd then you get 2,500 credits so keep racing. that is what i did and i now have 67,513 credits and im saving up for a better car. at the moment i have a lancer evolution v1 GSR T.M.E. they have really good handling and good speed too.
by the way dont get any type of skyline cos they cant keep up with the other cars... (i had a skyline [cost me 57,000 for the R34 type!] which i sold after a couple of races for only 14,000... it wasn,t good).
i hope i have helped you with all of your problems and given you some useful advise too

jimbob