If you're asking how to query data from more than 1 database in 1 query, I don't think there is a way to do this with a standard install, however I believe it is possible if you use contrib/dblink . At least that's what people tell me, when I've asked that question, however I have not needed to use it yet.
(I'm only available at the email address provided in my profile on weekdays, if you have questions or advice, during off hours use AIM). Also any views I provide here or on my website are mine and not representative of any views of my work, family, friends and sometimes even myself.
Also, remember that with PostreSQL 7.3, you have SCHEMA (with private tablespaces) support. This means that one database can actually look like as many "virtual" databases as you want, to different users. For example, if your database has a schema for 'public' (the default schema), you can also create a schema for 'devgroup'. In effect, both groups could have their own complete database, identical in tablenames, etc... but with different data. Then, whichever user has the appropriate permission (such as the 'postgres' root user) can query across both schemas in one query.