The marks on hands are stored in the database so you won't get them by importing hand history files to another database and the only way they can be directly transferred is via a
backup & restore of the entire database. You could also export your marked hands for review from a
custom report and you can then import and mark them in another database before importing the remainder of hands you want to transfer.
As far as exported notes are concerned if you import notes into another database then those notes are added to the existing notes in that database. Also if the same note exists in both databases then the note text is appended meaning that it will be doubled up so this isn't ideal if you are going to import notes from one database into another and then back again. You could delete notes before importing but there isn't a built in method to purge all manual notes so you'll need to use PGAdmin (which is in Start -> All Programs -> PostgreSQL) and run the following query:
TRUNCATE TABLE notes;
To do that double click on PostgreSQL x.y' (where x.y is your PostgreSQL version) and if your prompted for a password the default is "dbpass" (without the quotes), expand 'Databases' and then select your database. The query tool can be opened via its icon in PGAdmin or via 'Tools -> Query Tool' and then you can run the query using 'Query -> Execute'. I'd recommend backing up your poker data before making any changes since PGAdmin is connected directly to your database so take care not to make any other unintended changes to your data while using it.
Also if, for example, your desktop is always on then another option so you don't have to manually sync hands/marks/notes is to have the laptop sharing the same PostgreSQL/database as the desktop:
Guide: PostgreSQL Server Hosted on a Local Network