For the migration of Oracle Applications you'd better at first install Oracle Applications on the Solaris (install only the files : concurrent program, reports and forms (if the solaris erver is the applicaiton server)). Then import all the data, you've exported from the NT server.
Attention : before the export on the NT server don't forget to stop the concurrent managers.
I was invovled with several such projects for migrations .here are some of the DO's
1)The most importatnt first step is to take a Cold backup of your system.i mean the entire software including ur database datafiles and the oracle software.
2)Most important step TEST WHEATHER YOUR COLD BACKUP ACTUALLY WORKS BY RESTORING IT ON A IDENTICAL SYSTEM.I CANT EMPHASIZE THSI POINT MORE.
2)Since your planning to take change of database from oracle to oracle.I suggest you take an export of the full database .Craete a database on solaris using the solaris cd and import it into sun solaris after creating the database there.
3)Now you can go ahead and install the applications and binaries to which are platform specific.
4)Perform some tests on the migrated sun platform ...........
you can check the import log,check wheather all objects have been imported.....and run the application and see.
5)Take a cold backup of the new database on sun-OS.
thats it .Do thsi excersise on some holiday or when the tarffic is low.Just in case somethin goes wrong you can fall back upon your cold backup..