Theres a couple ways to do this.
1) Logon to www.heat.net for some seriously warpy gameplay. Its an IPX
emulator which transforms your internet connection into a virtual LAN. You
can get 2 or 3 people into a single race like this.
2) Logon to www.ten.net for some free NROS using their demo. You are
limited to only being able to race Atlanta and Watkins Glen, but it is
better than nothing. Best part tho is that you get to experience the real
nature of racing against live humans. Imagine going head to head against 20
other real people, all of whom will do whatever it takes to win.
In either case, get ready for some real bonehead moves by other racers as
they slide up into you as you are high or slip down onto you when you are
low. The real serious racers are either racing the full version of NROS on
TEN or are into GPL.