I would just create models for each table (script/generate model table_name), then get real familiar with 'set_table_name', and 'set_primary_key'. If they are using compound primary keys, then you'll need Dr Nic's 'CompoundPrimaryKey' gem.
I'd also recommend creating the associations manually and not using the 'magic models' plugin.
I've done it with our in-house SQL Server db's and it works fine...
Good Luck,
Rich C.