Of course you could always try it with a new (Intel) Mac, the Boot Camp beta, and Windows XP...
Somebody has to try this. Otherwise we can all wait for Leapard (OS X 10.5) to come out, as it will come with a (probably non-beta) version of Boot Camp.
Doesn't exactly solve your problem, but there's been enough OS interest hereabouts that it's worth mentioning.
BTW, some unofficial - and less than comprehensive - benchmarks on the above configuration are pretty interesting. Performance appears to be similar to a 'raw' XP installation.
Now, back to Linux. Any possibility that the Crossover version you have is different than what Sparx used? Also, outside of working with EA, any other issues with PostgreSql, either on their site or your installation? In particular, look for ODBC issues. Also, is there an OLEDB driver for PostgreSql yet? Perhaps that will work, although it might not help you if you are importing a database schema.
Let us know.