I don't think there is an NT equivilent. This is because Unix has the individual background processes (SMON, PMON, DBWR, LGWR, ARCH, etc) running separately. On NT, these processes are being run under the umbrella of the Oracle service. Unfortunately, just because the service is running does not mean that the instance is up or the database is open.
One possibility would be to have a nested block of code that tries to select * from dual. If you get any error out of this query, there's a really GOOD chance that the database isn't available!